studies of extraction, storage, and testing of pine pollen
TRANSCRIPT
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H. JOHNSSON W. LANGNER R I RIGHTER K. SATO
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INHALTSVERZEICHNIS
Induction of Polyploidy in Pines by means of
Colchicine Treatment. By Sin Kyu Hyun .... 25
TJber zwei Typen der Japanlarche (Larix leptolepis
Gord.) in Schleswig-Holstein. Von F. W. Frhr.
von Schrotter .33
Studies of Extraction, Storage, and Testing of Pine
Pollen. By J. W. Duffield 39
Buchbesprechungen .46
Referate 46
Ausgegeben im Marz 1954
Studies of Extraction, Storage, and Testing of Pine Pollen
By J. W. Duffield
Institute of Forest Genetics, California Forest and Range Experiment Station1)
(Received for publication, October 6, 1953)
Introduction
This report assembles the results of a number of small
exploratory studies on the extraction, storage, and viabi
lity testing of pollen of several species of pines. These stu
dies indicate clearly the need for more knowledge of the
physiology of pollen — particularly of the relation be
tween atmospheric humidity at the time of pollen shedding
and the subsequent reactions of the pollen to environmen
tal conditions.
1. The Importance of Extraction Humidity and its Control
The importance of humidity of the air in which dehi-
scence occurs has long been recognized. Lidforss (1899)
allowed flowers of a number of angiosperm species to shed
pollen under various humidity levels, and found that, in
general, pollen shed at the higher humidities was more
germinable and more resistant to moistening injury than
that shed at lower humidities.
On March 18, 1946, the writer set up a small test to de
termine the effects of extraction humidity on germinabi-
lity and storage properties of pollen of Pinus canariensis.
Unopened catkins were collected from branch tips from
which some pollen had already been shed. All material
was taken from a single tree. Equal numbers of catkins
were placed in each of four cylindrical wire baskets
set in funnels which led into small shell vials. Each
assembly was placed in a glass jar in which relative
humidity was maintained at 10 percent, 25 percent,
or 75 percent by sulfuric acid solutions. All jars
were then placed in a constant temperature cabinet
at 22° C. On March 28, the extractors were removed
from the constant temperature cabinet and shaken vigo
rously until no more pollen fell into the vials. The yield
of pollen and the change in length of catkins during the
10-day extraction period were:
Extraction hu.idity Pollen yield ,cc.)
10%
25%
50%
75%
.67
.77
1.00
.29
-10
0
+ 50
+ 75
After the catkins from the 75 percent relative humidity
extractor had been exposed to the relatively dry air of
the laboratory for a few minutes, they shed about 0.7 cc.
of pollen, which, however, was not used in the subsequent
tests of germinability and storage.
These findings appear relatively easy to interpret on
the basis that pollen shedding is the resultant of two pro
cesses: The biological process of growth and elongation
of the catkin axis and the physical process of rupture of
the sporangia. The growth of the catkin axis requires
water, which may be furnished by the vascular system to
catkins on the tree or by a humid atmosphere to catkins
') The California Forest and Range Experiment Station is main
tained by the Forest Service, United States Department of Agri
culture, in cooperation with the University of California at Ber
keley, California. The author's present address: College of Fore
stry, University of Washington, Seattle 5, Washington.
in an extractor. Rupture of the sporangia requires relative
desiccation of the sporangium walls by a rather low
humidity (50 percent or less in this test). This interpreta
tion is similar to the one arrived at by Scamoni (1938), who,
however, used catkin-bearing branches of P. silvestris
rather than detached catkins in his experiments. Very
likely, in nature, elongation of the catkin axis and rupture
of sporangia occur simultaneously, the first process sup
ported by moisture supplied through the vascular system
and the second promoted by high evaporation associated
with sunshine, wind, and high temperatures (Scamoni,
1938). It appears quite difficult to reproduce these condi
tions in any practical type of extractor, but there is pro
bably a good chance of bringing about these two processes
in sequence, by adopting an extraction schedule under
which the catkin axes are allowed to elongate at a relative
humidity of about 50 percent and a temperature of 25° to
30° C, followed by reduction of humidity to 10 percent or
25 percent to cause rupture of sporangia.
So much for the mechanics of pollen extraction. What
of the effects of extraction humidity on the viability of
the pollen? To answer this question, the pollen of P. cana
riensis extracted on March 28, 1946, was, on the same day,
subdivided into nine lots for each extraction humidity, and
stored at 0°, 10°, and 22° C. and at 10 percent, 25 percent,
and 50 percent relative humidity.
All 36 samples were tested by the vapor method2) on
November 12, 1946, two replications being set up. Fifty
grains of each treatment were counted in each replication,
making a sample of 100 grains per treatment. The results
are shown in Table 1.
Table 1
Germination of Pinus canariensis pollen stored 229 days
Storage conditions
Percent germination when
extraction humidity was
io% 25% I 50% 750/0"
Temperature 0° C.
10% humidity 67 68 68 I 5225% humidity 78 62 72 ! 1950% humidity 76 78 68 21
Temperature 10° C.
10% humidity ! 61 70 8225% humidity 76 68 7150% humidity ■ 64 89 33
Temperature 22° C. ■
10% humidity j 55 83 5725% humidity '' 55 39 4050% humidity 5 7 0
The results of this test may be summarized as follows:
Extraction at 75 percent relative humidity is disadvanta
geous regardless of how the pollen is stored subsequently.
It should be noted, however, that the pbllen extracted at
75 percent relative humidity was handled in a room with
a relative humidity of 30 percent to 50 percent when the
pollen was segregated into lots for the storage test. These
fluctuations in humidity, although brief, may have
influenced the germinability of certain lots.
18
4
13
0
0
*) Pollen testing methods are described in a subsequent section
of this paper.
During the course of the germination counts, certain ob
servations were made on the appearance, tube length,
forking, and bursting of each lot. Every sample of pollen
extracted at 75 percent relative humidity had a large
majority of grains which floated with bladders up and
had two or three large vacuoles generally arranged along
the short axis of these grains when viewed from above.
This was also true of the lot extracted at 50 percent and
stored at 22° C. and 50 percent. In general, pollen extrac
ted at 10 percent or 25 percent and stored at 0° C. or 10° C.
showed a high proportion of cytoplasmic extrusion both
from germinated and ungerminated grains. There was
less of this bursting in the lots extracted at 50 percent
and virtually none in those extracted at 75 percent.
Only by experiment can these findings with respect to
germinability of pollen extracted under various humidity
levels be related to the ability of such pollen to effect fer
tilization — particularly after storage of one year or more.
Nevertheless, it seems clear that variations in extraction
humidity such as those used in this experiment produce
effects which are certainly worth investigating further,
especially since variations of equal magnitude undoub
tedly occur between routine extractions of the pollen used
in breeding. Therefore, it should be worthwhile to deve
lop an extraction technique which will afford fairly accu
rate and individual control of the extraction humidity
(and temperature) of each lot of pollen. Such a technique
will not only be useful in conducting experiments to deter
mine optimum extraction conditions, but also, after these
are determined, it will be necessary in routine breeding
operations. It is quite possible that once pollen extraction
is better standardized and species requirements under
stood, many species crosses which have failed in the past
may be found possible. At any rate, it seems clear that
standardization of humidity and temperature at which
pollen is extracted must precede any careful work on pol
len storage and barriers to species crosses.
2. Pollen Storage
In 1945, samples of pollen of seven species of pines
were placed in storage by Dr. N. T. Mirov. Four levels of
temperature (0°, 5°, 10° and 22° C.) and four levels of rela
tive humidity (10%, 25%, 50% and 75%) were used. The
dates of collecting and storing of the pollen samples are as
follows:
Species
P. radiata D. Don
P. canariensis Smith
P. taeda L.
P. echinata Mill.
P. ponderosa Laws.
P. strobus L.
P. lambertiana Dougl.
Date collected
—
April 10
April 11
May 3
May 24
May 24
July 11
Date stored
February 24
April 18
April 18
May 10
July 2
July 2
August 8
In 1946, the germinability of these samples was deter
mined by dusting pollen from the storage vials onto mar
ked spots inside a Petri dish bottom. All sixteen storage
conditions were tested in a single dish, and two dishes
were set up for each species. The samples from each sto
rage condition were arranged in randomly-selected Latin
squares. Each Petri dish bottom so set up was then inver
ted into a Petri dish cover with enough water in it to
cover the bottom and provide a water seal, so that the air
in the dish was kept saturated with water vapor. The
dishes were then incubated at 25° to 28° C. for 48 to 72
hours. Germination percents were determined from 100-
grain samples, that is, the sums of two determinations of
50 grains each (Table 2).
Table 2
Pollen germinability — seven pine species
Species
P. radiata
P. canariensis
P. taeda
P.echinata
P. ponderosa
P. strobus
P. lambertiana
Date
of test
May 22,
1946
May 22,
1946
May 22,
1946
Oct. 15,
1946
Sept. 10,
1946
Oct. 15,
1946
Sept. 10,
1946
Days
stored
391
338
338
523
435
470
398
Storage
temp.°C.
0
5
10
22
0
5
10
22
0
5
10
22
0
5
10
22
0
5
10
22
0
5
10
22
0
5
10
22
Relative humidity
in storage
10% 25% 500/q 75<y0
Percent germinated
2
3
33
10
61
68
65
65
39
30
35
41
86
91
82
88
71
60
70
70
85
88
88
74
9
7
16
31
78
73
69
24
62
61
57
36
36
33
30
46
82
83
83
67
68
58
61
57
82
91
69
66
18
36
27
5
67
56
11
0
70
60
51
0
30
33
58
0
98
90
94
0
71
51
16
0
S3
81
36
0
11
28
6
0
1
0
0
0
30
4
0
—
7
0
0
0
60
4
0
0
0
0
0
0
13
0
0
0
0
0
0
0
In two respects these tests are quite consistent and
conclusive. First, storage at 75 percent relative humidity
is undesirable, regardless of temperature. Secondly, in all
species, storage at 50 percent relative humidity and 22° C.
is undesirable, and in most species, this is true of storage
at 25 percent relative humidity and 22° C. In one respect
the species tested seem to fall into two groups. P. radiata
and P. lambertiana pollen stored at 10 percent relative
humidity and at 0° and 5° C. showed very low germina
bility, whereas this effect was not found in the other five
species tested. In order to determine whether this effect
was real and not due to experimental errors, a repeat test
was made, October 18, 1946, with pollen of P. radiata
(Table 3).
Table 3
Germination percentages — Pinus radiata pollen stored for 540 days
Tempe
rature °C.
Germination when relative humidity
in storage was
10,% 25%
0
5
10
No.1)
0
0
1
0
0
0
7
0
0
7
14
13
• °/o2)
1
7
34
No.1)
18
16
24
20
22
moldy
22
19
21
23
25
21
°/o2)
78
84
90
No.1)
22
23
21
19
24
19
20
17
14
8
10
9
°/o2)
85
80
41
') Number germinated in a 25-grain sample.
2) Totals or germination percent.
40
Results of this test fully bear out the indications that
P. radiata pollen is sensitive to low-humidity, low-tempe
rature storage. It may be asked whether this is a matter
of actual species differences or is an effect of differences
in extracting and handling the pollen samples before they
were stored. Although some of the data in Table 1 make
it appear that low extraction humidity makes pollen more
sensitive to low-humidity storage, yet several repeat tests
with samples extracted and stored at low humidities fai
led to give consistent results. Therefore, this question
must remain open for the moment.
In discussing storage requirements, the results of the
present work should be related to previous findings.
Duffield and Snow (1941) found that storage at 0° or 4° C.
and 50 percent relative humidity was most favorable for
pollen of P. strobus and P. resinosa. The present work is
in general agreement with these findings, and supple
ments them to the limited extent that it shows that if
the optimum humidity is greater than 50 percent it cer
tainly is not as great as 75 percent. In this respect the pre
sent work differs from the findings of Johnson (1943),
who reported good germination for several pine and
spruce species after 12 months' storage at 2° C. and 75 per
cent relative humidity. In fact, he reported this condition
to be the optimum for one lot of P. strobus and one of
Picea glauca. This is an important difference, and the
reason for it should be investigated. Another of Johnson's
findings is in agreement with the present study, namely
that, "There is considerable specific difference in tole
rance of low humidity storage at both 2° C. and room tem
perature". However, it should be remembered that presu
med species and tree differences in Johnson's work, as
well as the present one, might in reality be traceable to
extraction differences. It is interesting to note that
Johnson states, "All material was stored for several days
over anhydrous calcium chloride prior to testing", but
does not specify extraction techniques. This preliminary
desiccation of the pollen might well account for the into
lerance to low humidity storage of most of his samples,
although, as previously noted, this question is still open.
In the study by Duffield and Snow (1941), pollen was
extracted by allowing catkins to open and shed on sheets
of paper spread out on tables in rooms with a relative
humidity of probably 25 percent to 40 percent, although
this was not stated in their paper. How these conditions
compare with those in the extractors used at the Institute
of Forest Genetics, (Cumming and Righter, 1948) would be
difficult to state, but probably extraction in an open
room occurs at a lower humidity than in a funnel-and-bag
extractor.
Another factor which should be kept in mind in com
paring Johnson's work with that reported here is that
different germination techniques were used. Johnson
sowed his pollen directly from the desiccators onto a moist
agar medium, whereas in the present tests, vapor germi
nation was used. The significance of this difference in
procedure will be discussed later.
Storage at 25 percent relative humidity appears to be
indicated by the present and previous studies on the basis
that this level of humidity has not been found injurious
to pollen of any pine species at low temperatures, and is
definitely preferable to 50 percent relative humidity when
it is necessary, because of limited cold storage space, to
store pollen at or near room temperature.
3. Pollen Testing
a. Importance of pollen testing
By testing of pollen is meant the determination of its
viability by means of artificial germination tests. It should
be recognized that testing pollen by means of artificial
germination is quite different from similar tests of seeds.
Our knowledge of the growth requirements of seedlings
is usually sufficient to enable us to predict from the
results of a germination test, the number of plants that
may be derived from a given lot of seed. With pollen, the
situation is quite different. The relationships between the
pollen grain and the intended maternal tissues are so
complex and little-known — especially in the gymno-
sperms, that artificial germination tests cannot be relied
upon to give positive information as to the fertilizing
potential of a sample of pollen. However, it seems reaso
nable to assume provisionally that pollen which cannot
be made to germinate by usual means or which, on germi
nation, shows unusually poor tube growth, is likely to be
ineffective in causing fertilization. Herein lies the present
practical value of pollen testing as a routine procedure in
breeding operations. Perhaps the coordination of pollina
tion and germination tests will enable us, in the future, to
make positive as well as negative predictions from ger
mination tests. At any rate, pollen extracted by prevailing
methods is often enough found to be non-germinable to
fully, justify routine testing if only to avoid waste of time
and materials which results when non-functional pollen is
used in breeding operations. An even more cogent reason
for routine testing is the likelihood of drawing incorrect
conclusions from the failure of certain attempted crosses
if non-functional pollen is used unwittingly.
b. Methods of pollen testing
Three main methods of germinating pollen have been
used. They are the hanging drop, agar gel, and vapor
methods. The hanging drop method has been described
by Righter (1939) and the agar gel method by Duffield and
Snow (1941). The vapor method is a modification of a tech
nique described by von Walderdorff (1924), who used
dried 10 percent gelatin solution on slides as a substrate
for the pollen. Moisture was supplied to substrate and
pollen by placing drops of sodium chloride solutions of
various vapor pressures near the pollen. As used by the
writer, this method is simplified to the extent of omitting
the gelatin and providing water vapor by the addition
of distilled water to the bottom of the culture dish.
The details of the method are as follows: A rubber
stamp consisting of a number of circles of 5 mm. inside
diameter arranged in rows and columns to form a
rectangle as in the method described by Righter (1939) is
used to stamp rings of vaseline into the inside of the
bottom (smaller part) of a Petri dish. These rings serve to
localize the pollen, which is dusted on the dry glass sur
faces within each ring. In order to achieve an even
dusting, the pollen is picked up on the end of a wood
applicator 1 mm. in diameter, which is then tapped over
the upper end of a vertical glass tube about 60 mm. long
and 5 mm. inside diameter. The tube is thrust through
the hole in a square plate of transparent plastic large
enough so that whatever part of the dish is being dusted,
the whole dish is protected from air currents and air-borne
contamination. A clean glass tube and a fresh applicator
are used for each lot of pollen. When all the pollen
41
samples have been dusted into the dish bottom, it is in
verted into the larger member of the dish, which has
enough water in it to provide an air lock. Incubation is at
26° C. to 28° C. This method may be readily transformed
into a hanging drop method by adding a drop of distilled
water to each ring before adding the pollen. Two diffi
culties are often encountered in setting up vapor germi
nation cultures. First, the pollen is likely to roll down the
sides of the glass tube rather than falling freely through
the air, resulting in a crescent-shaped deposit of pollen at
one side of the ring. Second, under some conditions, the
pollen, the glass tube, or both, may pick up a charge, so
that when the glass tube is withdrawn after the dusting,
the pollen flies all over the Petri dish bottom. This can
generally be avoided by withdrawing the tube slowly.
In relation to the vapor germination method, it is inter
esting to note that Kuhlwein (1937) reported that he was
unable to germinate pollen of Pinus silvestris or P. mon-
tana on clean glass in a saturated atmosphere, while gym-
nosperm pollens with swelling layers, such as Taxus, Cha-
maecyparis, Thuya, and Juniperus germinated well under
these conditions. In the present work, some vapor cul
tures have had so much condensation on the glass on
which the pollen grains were lying that they were for all
practical purposes hanging drop cultures — with this
important difference: the moistening of the pollen was
gradual. However, many of the cultures have been true
vapor cultures, the only visible water being on the sur
faces of the pollen grains and the immediately adjacent
glass. In fact, the optical properties of such cultures are
such that, in order to make germination counts readily,
condensation of a large amount of water within the rings
is induced by heating the bottom of the culture for a few
minutes. It is hard to reconcile this finding with Kuhl-
wein's (1937), failure to germinate pine pollen on glass in
saturated air.
c. Relation of testing method to extraction,
storage, and species
For the purposes of this discussion, the methods men
tioned above may be grouped into those in which the
pollen is transferred directly from storage to a wet germi
nation medium and the vapor method by which the pollen
is gradually moistened and finally wetted in an atmo
sphere saturated with water vapor. The results achieved
by these two general methods (Table 4) may be quite simi
lar or very different depending on species and condi
tions of extraction and storage.
Table 4
Germination of pollen of four pine species tested by drop and by
vapor methods
Species
P. canariensis
P. lambertiana
P. ponderosa
P. radiata
Germi
nation
method
Drop
Vapor
Drop
Vapor
Drop
Vapor
Drop
Vapor
Storage humidity')
10% 50%
Percent germination2)
60
72
23
66
28
84
16
8
70
84
73
70
89
92
80
78
Results of a test presented in Table 4 suggest that for
P. lambertiana and P. ponderosa the hanging drop method
is much more suitable for revealing the results of storage
at different humidities. Whether storage of pollen of these
species at low humidity would have an unfavorable effect
on fertilization comparable to that on germination in
distilled water remains to be tested. In the case of P.
radiata, storage at low humidity appears to depress germi-
nability whether the drop or the vapor method is used.
The drop method appears to give better germination with
pollen stored at low humidity, and, if significant, this
is an interesting reversal of the relations found in P. lam
bertiana and P. ponderosa. Finally, neither storage humi
dity nor germination method appears to affect the ger-
minability of P. canariensis pollen stored at 0° C. to nearly
the striking extent found with the other three species.
However, this difference may possibly be traced back to
conditions of extraction. To test this possibility an
experiment was set up with the same lots of pollen used
in the P. canariensis extraction humidity experiment.
Table 5
Germination of Pinus canariensis pollen tested by drop and by
vapor methods
Storage
Temp.
o°c.
22° C.
Humidity
10%
50%
10%
50%
Germination
method
Drop
Vapor
Drop
Vapor
Drop
Vapor
Drop
Vapor
Extraction humidity
10% 50%
Percent germination1)
72
78
72
79
67
74
34
22
51
72
69
79
9
77
0
0
J) Storage temperature 0° C. for each lot.
2) Each figure is based on 4 samples of 50 grains each.
*) Each figure is based on 4 samples of 50 grains each.
Results of this experiment (Table 5) suggest that low-
humidity extraction not only made P. canariensis pollen
more resistant to storage at high temperature and high
humidity, but made it indifferent to germination method
as well. Again, the question of which germination method
would lead to the correct evaluation of the pollen for use
in breeding must remain unanswered for the present.
However, the two experiments just reported leave little
doubt that as a laboratory procedure for revealing humi
dity treatment effects, the hanging drop method is far
more sensitive than the vapor method.
The findings of Duffield and Snow (1941), of Johnson
(1943) and of the present study suggest that pollen of some
conifer species is sensitive to low humidity storage. It
has been shown that extraction humidity may affect sto
rage responses of P. canariensis pollen, and now it appears
that the evaluation of these responses depends on germi
nation procedures. These results therefore indicate that
conclusions regarding species differences in storage
responses can be regarded as tentative and that their con
firmation awaits standardization not only of extraction
methods, but of germination techniques and probably, in
the end, of pollination tests as well. If hanging-drop or
other wet-medium tests are used, the problem of securing
a definite relation between the mass of the medium and
that of the pollen sown on it may be of great importance.
At present, the hanging drop method gives highly vari
able results — probably traceable to variations in density
of sowing. Some of these may be eliminated by increasing
42
the precision of the suspension and pipetting method of
setting up hanging-drop cultures which has already been
developed by Righter (1939). Pohl (1937a) obtained quite
uniform results in pollen grain counts with the use of
water suspension methods.
d. Relation of testing methods to previous
work on moisture relations of pollen
Several investigators have reported beneficial effects
from humidifying pollen before placing it on a wet ger
mination medium (Ruttle and Nebel, 1937; Pfeiffer, 1939).
Duffield and Snow (1941) showed that this effect was more
marked in the case of pollen of Pinus strobus and P. rest-
nosa stored at low humidities. The vapor method used in
the present studies is a logical development in view of
these findings. Nevertheless, it is not clear that the higher
germinability revealed when pollen is humidified before
wetting is any more indicative of the value of the pollen
for breeding than is the somewhat lower value determined
by wet-medium tests without preliminary humidifica-
tion. It must be emphasized that laboratory germination
tests should as soon as possible be correlated with polli
nation tests of samples of pollen stored under various
conditions. Certain difficulties in running comprehensive
tests of this nature should be recognized at the outset. As
Duffield and Snow pointed out: "Tests of the ability of
pollen to function in vivo — conclusively demonstrate
pollen viability if the results are positive. Negative
results of pollination tests are fully significant only when
the reproductive behavior of the plants used is well
known." Such tests may be "confounded by biological fac
tors such as incompatibilities and abortions since little is
known concerning these factors" in the pines.
e. Possible relations between moisture
history of pollen and r e spons e to growth
substances
Although laboratory tests of pollen germinability may
be of uncertain value for practical breeding operations,
they may prove to be powerful tools for increasing our
understanding of the physiology of pollen. Scattered bits
of evidence suggest that the great significance of moisture
history for the germination requirements of pollen may
be in some way related to auxins. Although pine pollen
has been shown to be a rich source of auxin (Gustafson,
1937), the work of Smith (1939), who found that pollen of
P. austriaca germinated in a 1 ppm. solution of indole-3
acetic acid but not in his controls, suggests that under cer
tain conditions the auxin in pine pollen may be inactiva
ted or unavailable. Many other investigators working with
pollen of many pine species have found it readily germin-
able under a wide range of conditions, and presumably,
in most cases, without externally supplied auxin. Thus it
seems possible that Smith's sample of pollen had been
treated in some manner which caused it to require auxin
for germination. Brink (1924) found that clumped pollen
grains put out tubes at a more rapid rate than grains iso
lated on the germination medium. This appears to be
consistent with the findings of Kuhn (1937), who discusses
at length the requirements of some pollens for specific
substances which may be secreted by the pistil or carried
by the pollen itself in minute quantities and shows that
pollens of this type may be germinated only on small
amounts of semi-solid media which will not, by leaching
and dilution, reduce the substance contributed by the pol
len below an effective concentration. Lidforss (1899) found
that the injury to pollen caused by wetting and sub
sequent drying was less if the grains were clumped. Smith
(1942) suggests that this may not have been so much an
effect of retarded drying as a matter of reduced aeration
possibly affecting oxidation and inactivation of auxins.
f . P o s sibilitie s of developing lab or at ory
criteria other than g er minab ility
So far, the whole discussion has dealt with germinabi
lity of pollen. As has been suggested, this property cannot
be considered to be, in itself, a reliable index of fertilizing
ability. Probably what germinability reveals is that a cer
tain percentage of grains is able to cross a certain func
tional threshold. No doubt, fertilization is some distance
beyond this threshold, but germination tests give little or
no information as to how much of this distance the germi
nated grains could cover in nature. In practice, at the
Institute, this lack has been recognized, and an effort
made to compensate for it by several means. These consist
of (1) noting the time elapsed between set-up of test and
germination counting, (2) noting length of pollen tubes as
a multiple of grain diameter, (3) estimating the percentage
of burst grains. It is probably fair to state that the latter
two types of data are the results of rapid ocular estimates
and that it would be unsound to base critical comparisons
of pollen lots on them except in cases of unusually large
differences. In such cases these differences would prob
ably be reflected in germination percentages.
For experiments designed to evaluate precisely extrac
tion and storage conditions, it should be possible to deve
lop measurements which would give more information on
the fertilizing potential of pollen than the enumerations
largely relied on up to present. It would seem that deter
mination of the rate of pollen-tube elongation should be
a relatively simple matter, and that once this rate is deter
mined, it might be shown to have a rather simple relation
to fertilizing potential. While the latter proposition is very
likely sound, the accurate determination of pollen-tube
elongation rates depends on refinements of technique
which have yet to be attained. One example of an attempt
to determine elongation rates will illustrate this. When
the germination percentages for P. radiata shown in
Table 2 were determined, measurements of pollen-tube
lengths were also made. These, together with germination
percentages, are shown in Table 6. In this table, the ger
mination percentage based on a sample of 50 grains is
given for each plate as is pollen-tube length, each value
being based on 10 measurements.
Table 6
Germination and pollen tube lengths1) of P. radiata pollen stored
391 days
Storage
temperature
o°c
5° C.
10° C.
Germ.Percent
Tube Length
Germ.Percent
Tube Length
Germ.Percent
Tube Length
Storage humidity
25%
Plate A
80
22.2
80
25.3
68
19.3
Plate B
76
33.2
66
32.4
70
34.8
Mean
78
Tin
73
28.9
69
27.1
50%
Plate A
66
19.2
48
17.4
8
21.4
PlateB
68
26.6
64
24.6
14
23.6
Mean
67
22.9
56
21.0
11
18.0
') Pollen tube lengths given in ocular micrometer units. One
unit equals 6.7 micra.
43
It will be noted that germination percents of the A and
B plates do not differ consistently, and that the A and B
plate percents are rather close to their means (Table 6). In
the case of pollen-tube length, however, it is clear that for
every storage condition under which germination occurred
in both plates, the growth rate in plate B was higher than
in plate A. This no doubt means that temperature was
slightly higher in plate B than in plate A during germina
tion and tube growth. In this particular test, the plates
were placed side-by-side on the top shelf of a seed germi
nating incubator running at 25° C. The uniformity of
conditions within the incubator appears to have left
something to be desired, but sufficient uniformity could
probably be attained only in an aircirculating incubator
with very precise thermostatic controls. At any rate, it is
clear that tube elongation is more sensitive to incubation
conditions than is germination percent. Analysis of variance
of the pollen tube lengths shows that the superiority of the
B plate series is highly significant, and further, that sto
rage at 25 percent relative humidity results in more rapid
pollen-tube growth than storage at 50 percent relative hu
midity (high significance). There was no significant diffe
rence in the effect of the three rather low temperatures on
pollen-tube growth. Scanning Table 6, it appears that an
evaluation of the storage methods by pollen-tube growth
would differ little from one based on germination percent
— both measures indicate that storage at 25 percent rela
tive humidity is somewhat superior to storage at 50 per
cent relative humidity. So far, it seems that little gain in
information has been achieved after a considerable in
crease in labor. Perhaps germination percent and pollen-
tube growth are highly and positively correlated. This
possibility should be studied further for if it proves to be
fact, there would be little utility in estimating pollen-
tube growth, at least for routine testing.
Another aspect of pollen cultures which may be related
to the fertilizing potential of pollen is the amount of bur
sting or cytoplasmic extrusion by pollen-grains and pol
len-tubes. This is at present noted in routine tests. Bur
sting of pollen-tubes is a phenomenon which has been
shown to be related to a wide variety of conditions of pol
len extraction Ltdforss (1899) and of storage and germina
tion techniques Kuhlwein (1937).
In the extraction experiment with pollen of P. canarien-
sis (Table 1) each germination count was accompanied by
a rating as to the amount of bursting. Practically all samp
les extracted at 10 percent or 25 percent relative humidity
showed bursting regardless of subsequent storage, while
very few of the samples extracted at 50 percent relative
humidity showed bursting.
In the storage and germination test reported in Table 4,
similar notes were taken on amount of bursting. The most
striking result was that all samples of P. lambertiana pol
len stored at 0° C. and 10 percent relative humidity and
germinated by the vapor method showed a high percent
of bursting, while little bursting was found among samples
of this species stored at 10 percent relative humidity and
germinated in a drop or stored at 50 percent relative humi
dity and germinated by either method.
It therefore appears that bursting is influenced by a
number of factors not yet understood or not controlled by
our present techniques. Perhaps when our pollen hand
ling techniques are further standardized, studies of bur
sting will be of some value.
Two other morphological observations were made du
ring the present study. Pollen which has been stored at
75 percent relative humidity appears to float differently
from pollen stored at lower humidities. Generally, pollen
stored at 10 percent to 50 percent relative humidity (ex
cept that stored at 22° C. and 50 percent relative humidity)
floats with the bladders more or less to one side, while
that stored at 75 percent relative humidity floats with
the bladders up so that when viewed from above, each
grain is symmetrical along two axes. One is immediately
struck by the symmetrical and uniform appearance of such
a lot of pollen when one views it under the microscope in
a hanging drop. In the extraction experiment reported in
Table 1, it was noted that all pollen extracted at 75 percent
relative humidity, regardless of subsequent storage, sho
wed a very high percentage of grains which floated with
bladders up, and in addition had two or three large va-
cuoles in the central part of the grain between the blad
ders. These two visible criteria may be of some value in
detecting promptly lots of pollen which have been subjec
ted to unfavorable extraction or storage conditions. How
soon pollen takes on these aspects after being placed in a
drop has not yet been determined.
During the storage experiments reported in Table 2 it
was noted, especially when making the tests of P. ponde-
rosa and P. lambertiana, that pollen stored at 75 percent
relative humidity and at 50 percent relative humidity and
22° C. took up water from the saturated atmosphere of the
culture dish very much more rapidly than did the other
samples of pollen. In this particular test, the incubation
temperature was between 20° C. and 25° C. and no conden
sation occurred in the tops of the dishes. The low humidity
samples appeared quite dry to the naked eye after two
days, at which time condensation was quite noticeable on
the high humidity samples. None of this latter pollen ger
minated, but uniformly presented the symmetrical ,,blad-
ders up" appearance.
Conclusions
The principal conclusion which can be drawn from these
studies is that pine pollen, although notoriously more long-
lived than many angiosperm pollens, is quite sensitive to
its temperature and moisture environment. This implies,
for further studies, that temperature and humidity should
be under control during extraction in order to obtain pol
len which will give reproducible results in storage studies.
Recent studies of conifer seeds have pointed to the same
conclusion as regards seed storage.
Aside from the purely technical implications for future
empirical studies of pollen handling, the present report
indicates that many basic aspects of pollen physiology and
biochemistry need exploration.
Zusammenfassung
Titel der Arbeit: Untersuchungen ilber Extraktion, Auf
bewahrung und Priifung von Kiefernpollen. — Ergebnisse
mehrerer Einzeluntersuchungen, die die Extraktion, die
Aufbewahrung und die Priifung der Lebensfahigkeit von
Pollen verschiedener Kiefernarten zum Gegenstand hat-
ten, werden zusammengefai3t. Sie sollen zugleich den Aus-
gangspunkt fur spatere Arbeiten uber die Pollenphysiolo-
gie bilden.
Den Einflufi der Feuchtigkeit wahrend der Pollen-Ex-
traktion behandeln die ersten Versuche mit Pinus cana-
44
riensis. Im Verlauf einer lOtagigen Extraktionsperiode bei
50% Luftfeuchtigkeit erbringen die Katzchen den hochsten
Pollenertrag, gleichzeitig verlangern sich ihre Achsen um
50%. Bei 10%iger Luftfeuchtigkeit verschlechtert sich das
Ergebnis, und die Achse verkiirzt sich um 10%. Die Katz
chen in 75%iger Luftfeuchtigkeit schiitten den grofiten Teil
des Pollens erst nach Abbruch des Versuches im trockenen
Labor-Klima. Zwei Erscheinungen lassen sich beim Polli-
nierungsvorgang trennen: 1. der biologische Prozefi der
Katzchenverlangerung und 2. der physikalische Prozefi
des Reifiens der Mikrosporangien. — Die Abhangigkeit
der Lebensfahigkeit des Pollens von der Hone der Extrak-
tionsfeuchtigkeit beurteilt ein Pollenaufbewahrungsver-
such von 229 Tagen mit variierten Feuchtigkeits- und
Temperaturverhaltnissen in jeweils 2 Wiederholungen.
Jede Probenahme umfaBt dabei 50 Pollenkorner, also 100
bei jedem Aufbewahrungsbeispiel (s. Tab. 1). 75%ige rela
tive Luftfeuchtigkeit bei der Extraktion des Pollens scha-
det der Keimfahigkeit bei jedem Aufbewahrungsklima.
Hohere Keimfahigkeit wird in alien Fallen bei geringerer
Extraktionsfeuchtigkeit erzielt. Die Nachpriifung der er-
haltenen Zahlen im Befruchtungsexperiment muB spater
erfolgen. Ebenso muB eine weitere Vervollkommnung der
Extraktionstechnik erreicht werden.
Der Klarung von Zusammenhangen zwischen den Auf-
bewahrungsbedingungen und der Keimfahigkeit des Pol
lens dienen andere Experimente mit 7 verschiedenen Kie-
fernarten (Aufbewahrungszeit etwa 1 Jahr und mehr).
Vier Temperatur-Varianten (0°, 5°, 10°, 22° C) mit je vier
verschiedenen Graden relativer Feuchtigkeit (10%, 25%,
50%, 75%) werden bei alien Arten verglichen (Tab. 2).
75%ige relative Feuchtigkeit bei der Aufbewahrung ist auf
jeder Temperaturstufe unerwiinscht; 50% ist ebenso un-
zweckmafMg, wenn bei 22° C aufbewahrt wird; bei den
meisten Arten auch 25% bei 22° C. Eine andere Tendenz
zeigen dagegen P. radiata und P. lambertiana, die bei 10%
und 0° bzw. 5° C die schlechtesten Keimergebnisse brin-
gen. Offen bleibt dabei, ob fur dieses entgegengesetzte
Verhalten womoglich die niedrige Extraktionsfeuchtigkeit
bei der Pollengewinnung verantwortlich sein kann. — Als
allgemeines Ergebnis ist feststellbar, dafi der Pollen aller
Kiefernarten bei 25% relativer Feuchtigkeit und niedri-
gen Temperaturen ohne Schaden aufbewahrt werden
kann und dafi dieses Verfahren einer Aufbewahrung bei
50% und Zimmertemperatur vorzuziehen ist.
Die Pollenpriifung mit Hilfe kunstlicher Keimteste wird
kritisch beurteilt. In ihrer bisherigen Form sagen sie nicht
ohne Einschrankung iiber die Befruchtungsfahigkeit des
Pollens aus, und sie miissen kiinftig mit Ergebnissen von
kontrollierten Bestaubungsversuchen verglichen werden.
Zur Pollenkeimung im Laboratorium wird eine Dampf-
methode (vapor method) angewendet. Die gewunschte
Dampfspannung erzeugt man durch Zusatz von destillier-
tem Wasser auf den Boden der Kulturschale. Die Keimung
erfolgt bei 26° bis 28° C. Die Methode selbst ist von Righter
(1939) beschrieben worden. In der Tab. 4 stehen die mit
dieser Methode erzielten Keimerfolge den Ergebnissen
der Pollenkeimung im ,,hangenden Tropfen" gegenliber.
Die dortigen Zahlengruppen unterscheiden sich je nach
Objekt voneinander und lassen keine allgemeine Bezie-
hung zum Aufbewahrungsklima des Pollens erkennen. U.
a. hat eine niedrige Extraktionsfeuchtigkeit bei dem Pol
len von P. canariensis eine hohe Resistenz gegen die Ein-
fliisse hoher Temperatur und Feuchtigkeit bei der Pol-
lenaufbewahrung zur Folge, unabhangig von der verwen-
deten Keimmethode. Die wichtige Frage nach der besten
Keimmethodik fur Ziichtungszwecke kann durch den Ver-
gleich beider Versuche nicht beantwortet werden. Wo
moglich scheint in manchen Fallen die Tropfen-Methode
vorteilhafter zu sein. Die Ergebnisse aller Einzeluntersu-
chungen lassen es ganz allgemein zweifelhaft erscheinen,
daB den Laboratoriumspriifungen der Pollenkeimfahig-
keit fur Ziichtungszwecke iiberhaupt ein Wert beizumes-
sen ist. Dagegen konnen sie aber den Ansatzpunkt fur eine
weitere Erforschung der Pollenphysiologie darstellen. In
diesem Zusammenhang werden einige Literaturdaten be-
sprochen. — AuBer der Pollenkeimfahigkeit lassen sich
auch andere Kriteria zur laboratoriumsmaBigen Pollen-
beurteilung heranziehen. Die Messung der Pollenschlauch-
langen erweist sich dazu als mogliche Grundlage. Nach
der Aufbewahrungszeit von 391 Tagen variieren z. B. die
mittleren Pollenschlauchlangen von P. radiata in positiver
Korrelation mit den Keimprozenten der Versuchsglieder
(Tab. 6). Als weitere Beurteilungsmomente konnen auch
Beobachtungen uber den Umfang des Platzens von Pollen-
schlauchen oder des Austrittes von Plasma aus den Pollen-
kornern Verwendung finden. Versuche mit P. canariensis
und P. lambertiana zeigen allerdings, daB das Platzen der
Pollenschlauche von mehreren, heute noch unbekannten
Faktoren abhangt.
Die Erfahrungen mit dem von Natur aus langlebigen
Kiefernpollen verdeutlichen in alien Fallen andererseits
seine groBe Empfindlichkeit gegen Temperatur und Feuch
tigkeit. Beiden Faktoren muB deshalb besonders bei der
Pollenextraktion groBe Beachtung geschenkt werden. Nur
solche Aufbewahrungsversuche haben einen Wert, deren
Ergebnisse sich reproduzieren lassen. Dies ist jedoch erst
dann erreichbar, wenn das Gebiet der Pollen-Physiologie
und der Pollen-Biochemie neu bearbeitet wird.
Literature Cited
Brink, R. A.: The physiology of pollen. IV. Amer. Journ. Bot. 11,
417—436 (1924). — Cumming, W. C, and Rihgter, F. I.: Methods used
to control pollination of pines in the Sierra Nevada of California.
U. S. Dept. Agric. Circular No. 792, 18 pp. (1948). — Duffield, J. W.,
and Snow, A. G., Jr.: Pollen longevity of Pinus strobus and Pinus
resinosa as controlled by temperature and humidity. Amer. Journ.
Bot. 28, 175—177 (1941). — Gustafson, F. G.: Parthenocarpy induced
by pollen extracts. Amer. Journ. Bot. 24, 102—107 (1937). — Johnson,
L. P. V.: The storage and artificial germination of forest tree
pollen. Canad. Journ. Res. 21, C, 332—342 (1943). — Kuhlwein, H.:
Zur Physiologie der Pollenkeimung, insbesondere der Frage nach
dem Befruchtungsverzug bei Gymnospermen. Beih. Bot. Cen-
tralbl. 57, A, 37—104 (1937). — Kuhn, E.: Zur Physiologie der Pollen
keimung bei Matthiola. Planta 27, 304—333 (1937). — Lidforss, B.:
Weitere BeitrSge zur Biologie des Pollens. Jahrb. wiss. Bot. 33,
232—312 (1899). — Pfeiffer, N. E.: Life of Gladiolus pollen prolon
ged by controlled conditions of storage. Contrib. Boyce Thompson
Inst. 10, 429—440 (1939). — Pohl, F.: Die Pollenerzeugung der Wind-
bltiter. Beih. Bot. Centralbl. 56, A, 365—470 (1937 a). — Pohl, F.:
Die Pollenkorngewichte einiger windbliitiger Pflanzen und ihre
okologische Bedeutung. Beih. Bot. Centralbl. 57, A, 112—172
(1937 b). — Righter, F. I.: A simple method of making germination
tests of pine pollen. Journ. Forestry 37, 574—576 (1939). — Ruttle,
M. L., and Nebel, B. R.: Storage experiments with pollen of cul
tivated fruit trees. Journ. Pomol. and Hort. Sci. 14, 347—359 (1937).
— Scamoni, A.: Uber Eintritt und Verlauf der mSnnlichen Kiefern-
bltite. Zeitschr. Forst- u. Jagdwesen 70, 289—315 (1938). — Smith, P.
F.: The influence of 3-indole acetic acid on pollen germination.
Science 90, 165—164 (1939). — Smith, P. F.: Studies of the growth of
pollen with respect to temperature, auxine, colchicine and vita
min Bi. Amer. Journ. Bot. 29, 56—66 (1942). — Walderdorff, M. v.:
Uber die Kultur der PollenschlMuche und Pilzmyzelien auf festem
Substrat bei verschiedener Luftfeuchtigkeit. Bot. Archiv 6, 84—110
(1924).
45
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GriegstraOe 100
Frankfurt a. M.*Niederrad
PostsdilieGfach 84
Mttndien 42
Aindorfer StraCe 93
Die japanische LarcheEine biologisdvertragskundliche Untersuchung
Von Dr. Reinhard S c h o b e r
o. Professor der Forstwissenschaft aa der Forstlidien Fakultdt der Universitat GOttingen und Leiter der NiedersSdisisdien Forstlidien Versudisanstalt
XII und 212 Seiten mit 82 Abb. und 55 Tabellen im Text und einem 46seitigen Tabellenanhang
kart. 15,— DM, Leinen 16,80 DM -
Die guten Erfahrungen mit den ersten Versuchsanbauten der
Japanlarche um 1890 fuhrten zu einer standigen Vermeh*
rung der Anbauflache dieser Holzart, die heute allein in
Westdeutschland schon auf 11000 ha vertreten bt.
Der Verfasser gibt in einer Monographic der Japanlarche
den ersten eingehenderen Beridit uber das biologisdie und
ertragskundlidie Verhalten dieser Holzart in Peutschland.
DieGrundlage dieser Beurteilung bilden umfassende Unter^
sudiungen in alien westdeutsdien Landern, deren Ergebnisse
jeweils den bisherigen Erfahrungen in Japan, in Deutsdi;
land und anderen europaisdien Landern gegeniibergestellt
werden.
lm einzelnen wurden unter anderem untersudit: die Stand'
ortsanspruche im naturlidien Areal und im kunstlidien
Anbaugebiet Nordeuropas, die Anfalligkeit gegen Krank^
heiten und Schadenswirkungen, insbesondere gegen den
Lardienkrebs, das waldbauliche Verhalten im Rein**
und Misdibestand, die Fragen der Begrundung und Durdv
forstung, die Sdiaftform, Astigkeit, Verkernung und der
Rindengehalt. In einem besonderen Absdinitt wurden die
japanische und europaische Larche in ihren Eigen^
schaften gegenubergestellt, wobei die friiheren Untersus»
chungen des Verfassers iiber Larix europaea Verwendung
finden. Dieser Vergleidi vermittelt wesentlidie Gesidits<»
punkte zu der Frage: japanisdie oder europaisdie Larche?
Die Beurteilung der Zuwachso und Ertragsleistung
wurde auf Erhebungen an Probestammen, einmalige Be^
standsaufnahmen und die langfristige Beobaditung von
Versuchsflachen gegrundet. Hierbei wurden der Zuwachs<»
gang des Einzelstammes untersudit und Massentafeln,
Formzahltafeln und Ausbaudiungsreihen gewonnen. Die
frtragsleistung der Japanlarche im Reinbestand wurde
durch Ableitung von Ertragstafeln fur 2 Ertragsklassen beimaGiger und starker Durdiforstung defuiiert, wahrend be*'
sondere Untersuchungen der Erkundung des Zuwachses im
lapanlarchen^Mischbestande dienten. Den AbsdiluG
bilden Erhebungen uber den Sortiments* und Wert^
ertrag der japanischen und europaisdien Larche.
Das vielseitige Forschungsergebnis diirfte ein guter Ratgeber
sein fur einen erfolgreichen weiteren Anbau der Japanlarche.
Zu beziehen durch jede Budihandlung
J. D. Sauerlander's Verlag, Frankfurt a. M. I
Allgemeine Forst? und Jagdzeitung125. Jahrgang
Unter Mitwirkung der Mitglieder der Lehrkorper von Freiburg i. Br. und Hann. Miinden und
Prof. Dr. G. B a a d e r und Oberforstmeister Dr. F.E. Eidmann .
herausgegeben von
Dr. E. Zentgraf,
o. Prof, der Forstwissenschaft an der
Universitat Freiburg i. Br.
Dr. H. Lemmel,
o. Prof, der Forstwissenschaft an der
Universitat Gottingen
Erscheinungsweise: Zweimal im Vierteljahr
Erscheinen des Jubilaums-Jahrgangs: Der Jubilaums-Jahrgang erscheint in 10 Heften in der Zeit
vom 1. Oktober 1953 bis 31. Dezember 1954
Bezugspreis: 7,20 DM im Vierteljahr zuzuglich V ersandspesen
Im Jubilaums-Jahrgang sind bis jetzt erschienen:
Heft 1: JubilSumsheft Herausgeber: Prof. Dr. E.
EntwicMungslinien und Gegenwartsprobleme der
deutschen Forstpolitik. Von Prof. Dr. Dr. Kurt
Mantel. — 12 Jahre Waldbauseminar an der
Universitat Freiburg i. Br. Von Prof. Dr. E.
Zentgraf. — Carl Philipp Arnsperger. Zu sei-
nem 100. Todestag. Von Dozent Dr. R. B. Hilf.
— Der Wald in der Landesgeschichte. Von Dozent
Dr. R. B. Hilf. — Die Bedeutung der Baum-
Heft 2, Sonderheft, Waldbau Hefausgeber: Prof.
Notwendigkeit der Mitberucksichtigung geschicht-
licher Methoden in der vegetationskundlichen
Forschung. Von Prof. Dr. Leo Tschermak. —
Die Rolle der Nebenbaumarten im Wirtschafts-
wald. Von Prof. Dr. H. L e i b u n d g u t. — tlberdie Kennzeichnung der Durchforstungsweise. Von
Prof. Dr. K. Olberg. — Umwandlung hiebs-
Heft 3, Sonderheft, Forstpolitik Herausgeber: Prof. Dr.ELemmel:
Zentgraf und Prof. Dr. H. Lemmel:
morphologie fiir .die Holzartenwahl in Trocken-
gebieten. Von Dr. Jofg Barner. — Arbeitenaus der Freiburger Schule. Von Dozent Dr. M.
P r o d a n. — Unterlagen fiir den Anbau west-
amerikanischer Nadelholzarten in Deutschland.
Von Prof. Dr. F. K. Hartmann, Landforst-
meister F. Querengasser und Dr. G. Jahn.
Dr. E. Zentgraf:
reifer Fichten- (Kiefern-) Bestande in Mischbe-
stande. Ein Versuch. Von Prof. Dr. K. VanBe
it o w . — Die Snoqualmie-Douglasie, die Dougla-
sie der Zukunft. Von Forstassessor Roland Boi-
s e 11 e. — Bildliche Darstellung des Bestands-
gefiiges. Von Prof. Dr. Dr. J. N. Kostler.
H a s e 1. — Die Bereicherung einheimischer Wal-
der mit fremdlandischen Holzarten. Von Forst-
meister W. Fabricius. — Der deiitsche Wald
in der Bodenreform. Von Prof. Dr. H. L e m m e 1.
neuzeitliche Aufgaben und Arbeitsmetho-
den der forstwirtschaftspolitischen Wissenschaft.
Von Prof. Dr. V. Dieterich. — Volkswirt-
schaftliche Leistungen und Leistungsmoglichkei-
ten im Kleinprivatwald. Von Dozent Dr. K.
Heft 4, Sonderheft, Forstliche Betriebswirtschaft und ForsteinriditungGast-Herausgeber: Prof. Dr. K. Abetz:
Betriebswirtschaftliche-Betriebstechnische Ein-
heiten und Zielsetzungen. Von Prof. Dr. V. D i e -
t e r i c h. — Probleme der Gewinnermittlung in
forstwirtschaftlichen Betrieben fiir Zwecke der
Einkommensteuer. Von Prof. Dr. J. S p e e r. —
Forsteinrichtung als Schule des Denkens. Von
Oberregierungsrat Dr. Wilhelm Mantel. —
Die Kontrollidee in der Schweizer Forstwirt-
schaft Von Prof. Dr. A. Kurth. — Die Wald-
standsaufnahme in Osterreich. Von Ministerial-rat Dr. Anton Horky. — Der ertragsgeschicht-
liche Zuwachs und seine Bedeutung. Von Prof.
Dr. K. A b e t z .
Es erscheinen ferner folgende weitere Sonderhefte:
Ertragskunde, Gast-Herausgeber: Prof. Dr. G. Mitscherlich
Forstschutz, Gast-Herausgeber: Prof. Dr. E. Merker
Bodenkunde, Standortslehre, Gast-Herausgeber: Prof. Dr. W. Wittich
Forstbenutzung, Gast-Herausgeber: Prof. Dr. H. Mayer-Wegelin
J. D. Sauerlander's Verlag, Frankfurt am Main I