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1、Lot.Mag.Tokyo90:129—1411977AnatomicalStudyontheShootApexofOsmundajaponicaThunb.关于紫萁枝条尖的解剖研究RYOKOJMAIcHI*Depart,eentofBiology,FacultyofScience,OckanomizuUniversity,Oktsuka,Bunkyo-ku,Tokyo112Theontogeneticandseasonalvariationsintheorganizationoftheshootapicalmeristemo
2、fOsmundajaponicaThunb.wereinvestigated.Themeristemiscomposedofanapicalsegmentationzone(SZ),amothercellzoneofthestele(MS)andaperipheralzone(PZ).Asingleapicalcellismostlydiscernibleinallseasonsthrooghoutthewholeprocessofontogenyobservedinthepresentstudy.Theapicalcelli
3、susuallyfour-sided,nearlytriangular,witharegularsegmentationpatternintransverseview.However,itissometimesaccuratelythree-sidedwithahighlyregularsegmentationpatternintheactiveseason,whileitisoftenfour-sided,nearlytrapezoidorfive-orsix-sided,withalessregularsegmentati
4、onpatternintheinactiveseason.Thesizeoftheapicalcellrepresentedbyitsfreesurfaceareaincreaseswiththeincreaseinsizeoftheplantbodyintheyoungplants.However,intheadoltplants,thesizeoftheapicalcellissmallerintheactiveseasonandlargerinthedormantseason.Theorganizationpattern
5、oftheshootapicalmeristemof0.joponicadoesnotshowanintermediatetypebetweentheeusporangiateandtheleptosporangiateferns,buttheleptosporangiateferntype.对于紫萁枝条顶端分生组织的介体娄生和季节变异的机体形成过程我们已有所了解。其分生组织包括顶端分节区域（SZ），中柱的母细胞区域（MS）和外周区域（PZ）。在目前的研究中指出单个顶端细胞在个体发生整个过程的各个时期大部分可被识别。在横向视野
6、中顶端细胞通常是接近三角形的四边形，具有一个规律性的分节模式。然而，有时候它会是具有高度规律分节模式的标准三边形在生长活跃期，在生长不活跃的时期它又经常是四边形，接近梯形或五边六边形，并罕有规律分节模式。在幼年植物中，顶端细胞的大小是由它的自由表面积随着植物体大小的增长而增长来表现的。然而，在成年植物中，顶端细胞的大小在生长活跃期会变小，在休眠期会变大。紫萁的枝条顶端分生组织的构成模式不能说明它是存在于厚囊蕨类和薄囊蕨类之间的中间型，而是属于薄囊蕨类植物。Shootapicalpatternsinpteridophytesha
7、vearousedarenewedinterestinrecentyearsinregardtothezonationandtissuedifferentiationwithintheapicalmeristem(McAlpinandWhite,1974;Hébant-Mauri,1975)andtotheactivityoftheapicalcell(IJ’Amato,1975).WithregardtotheshootapicesoftheFilicales,itisgenerallyacceptedthatinthele
8、ptosporangiatefernsthereisclearlyasingleapicalcell,usuallywiththeshapeofatetrahedron,whileintheeusporangiatefernsasexemplifiedbytheMaratti
