Atlas of Woody Plant Stems

Evolution, Structure, and Environmental Modifications

Bearbeitet vonFritz H. Schweingruber, Annett Börner, Ernst-Detlef Schulze

1. Auflage 2008. Buch. x, 229 S. HardcoverISBN 978 3 540 32523 9

Format (B x L): 21 x 29,7 cmGewicht: 975 g

Weitere Fachgebiete > Chemie, Biowissenschaften, Agrarwissenschaften >Biowissenschaften allgemein > Ökologie

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MODIFICATIONOFSHOOTS:LONGANDSHORTSHOOTS

The formation of plant crowns depends on theinitiation of buds and the variable growth of

twigs(Roloff2001).Sometwigsgrowfastandturninto long shoots; others grow slowly andbecomeshortshoots (7.1-7.5).Geneticandecological fac-

7.1ShortshootsonalongOne-seedHawthornshoot(Crataegusmonogyna).

7.2Cross-sectionofa longBlackLocust treeshoot(Ro-binia pseudoacacia). In the large rings, the latewood iswideanddense.

7.3Cross-sectionofashortBlackLocusttreeshoot(Rob-iniapseudoacacia).Intheverysmallrings,thelatewoodisalmostabsent.

tors determine the growth of twigs. The geneticinfluenceisveryobviousinsomeconifers,suchaslarch (7.7-7.10). Annual longitudinal growth maybe determined by bud-scale scars. Annual radialxylemgrowthisindicatedbytheringwidth(7.6).

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7.5Cross-sectionofa long shootofSilverBirch (Betulapendula)withlargerings.

7.4Cross-sectionofashortshootofBeech(Fagussylvatica).Thenarrowringsaretypicalofthisshortshoot.Thefirstwideringsindicatethatthetwigstartedasalongshoot.

7.6 The transition from a long-shoot-phase to a short-shoot-phaseinSilverBirch(Betulapendula)isreflectedinasuddenradialgrowthchange.

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7.7Shortshootsandmaleflowersonahorizontal, longshootofEuropeanLarch(Larixdecidua).

7.8Cross-sectionofashortshootofaEuropeanLarchtree(Larixdecidua).Thebarkisextremelythickinrelationtothexylem.The18-year-oldshortshootdoesnotcontainanyringsinthexylem.

7.9 Longitudinal section of a short shoot of EuropeanLarch(Larixdecidua).Thechambersinthepithrepresentannualshoots.

7.10Microscopic section of a twig of Common Beech(Fagussylvatica).Theverysmallringsinthecenterindi-cate that the twigremained in theshort-shoot-phase formanyyears.Duetosuddenlyimprovedlightconditions,afteraneighbouringtreehadbeenfelled,thetwigwentintoalong-shoot-phase.This isshownbythelargeringstowardstheperiphery.

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MODIFICATIONOFSHOOTS:SHEDDINGNEEDLES,MALEANDFEMALEFLOWERS

Afteracertainnumberofyears,evergreenconi-fersshedtheirneedles,maleflowers(7.11)and

cones.Atfirst,thesepartsareisolatedfromthetwig,then dropped and, finally, the wound becomesovergrown. The exact position of this wound isdatabledendrochronologically.Onthebasisofthatobservation,Jalkanenetal.(1995)wereabletodatethelifeexpectancyofneedlesoveratime-periodofmorethan100years.

Programmedcelldeathdetermineswhen thenee-dles are shed.They break off at an anatomicallyfixedposition(theneedlebase),afterthistissuehasdried. The life expectancy of pine needles variesfrom 3 to 15 years (7.12).Male flowers are shedafterafewweeks(7.13),whereastheconesremainonthetwigformanyyears(7.14).

7.11 Spirally arrangedtraces of male flowers ona long shoot of MountainPine(Pinusmugo).

7.12 Needle trace on a twig of Mountain Pine (Pinusmugo).The needlewas alive for over eight years.Aftersheddingoftheneedle,callusformedfortwoyears.Forafewyears,theovergrownneedletracemaystillbeidenti-fiedasabentlatewoodzone.

7.13OvergrowntraceofamaleflowerofMountainPine(Pinusmugo).This flower had originated in the pith; itwasa latent shoot.The twig shed theflowerduring thefirst year’s latewood formation. Calluswas formed untilthefollowingyear.Theopenspaceintheperidermindi-cateswheretheflowerwasshed.

7.14OvergrowntraceofafemaleconeofMountainPine(Pinusmugo).Itremainedonthetwigforfouryearsandwasshedduringearlywoodformation.Thetwofollowingyearsarecharacterizedbycallusformation.Ittookseveralyearsuntilthedifferentiationprocessnormalizedagain.

7.11 Spirally arrangedtraces of male flowers ona long shoot of MountainPine(Pinusmugo).

SheddingoftwigsseeAbscissionpp.64.

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MODIFICATIONOFSHOOTS:THORNSANDSPINES

Averyeffectivemethodforaplanttoresistgraz-ing is the formation of spins and thorn. Theevolutionary pressure of herbivoreswas so strongthat stems, branches, twigs and leaves developedthorns (7.15-7.20),and thebarkdevelopedspines(7.21,7.22).Alldefencemechanismsarebasedon

7.15Transformationfromashortshoot(floweringpart)toathorn(tip).Blackthorn(Prunusspinosa).

7.17 Cross section of a thorn of Blackthorn (Prunusspinosa)withtwoleaves.Characteristicisthepithandtheabsenceofvessels.Thefibersareverythick-walled.

7.16HoneyLocust(Gleditsiatriacanthos).Ashoottrans-formedintoathorn.

extremecellwallgrowth,thelignificationoffibersandparenchymacells(7.17),andtheformationofa sharply pointed tip.Thorns aremetamorphosedshortshootsorleafveins(7.19,7.20),forexampleinBerberis.Spinesformfromcortexcells,forexam-pleinrosetwigs(7.21,7.22).

7.18Crosssectionofathornonaoneyear-oldlongshootof anAppleTree (Malus sylvestris).Characteristic is thepith and the presence of very small vessels (polarizedlight).

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