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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
Zu Inhaltsverzeichnis
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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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7MODIFIC
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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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MODIFICATIONOFSHOOTS:LONGANDSHORTSHOOTS
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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