XXXIII] 



ANATOMY 



297 



Fig 151 B) It is also absent from the very large stem of C medidlaris, 

 shown half-size in Fig. 559- Since that stem is more than twice the diameter 

 of the stem of C. Imrayana dissected by De Bary, it follows that here 

 complexity is not directly related to size alone. 



In the Cyatheaceae the adult leaf-trace is given off directly as a number 

 of disintegrated strands, which spring from the lower margin of the leaf-gap 

 (Fig 560) This is a highly advanced state as compared with Gleichema ; but 

 Mctaxya and Lophosoria suggest intermediate steps in the amplification of the 



Fie ;^Q. Cyathea mechdlaris. Transverse section of stem, 

 with adventitious roots and leaf-bases cleared away, showing 

 the vascular system, with numerous medullary stranils. 

 {\ natural size.) 



trace in the formation of the lateral involutions opposite to the pneumatodes, 

 and in its disintegration (compare Vol. I, Fig. 161). There is some variation in 

 the degree of disintegration of the leaf-trace, especially in the upper part of 

 the leaf It is interesting to note that examples of this are specially eviden 

 in Alsoplnla, a genus which on other grounds may be held as the mos 

 primitive of the three (Fig. 561). (Compare Bertrand et Cornaille, La Masse 

 libcro-ligncuse clement aire des Filicinees. Lille, 1902.) 



The ontooenetic development throws light on the evolutionary history of the complicated 

 valcular vstem of these stems. Stenzel had already in 1861 shown in AlsopJula aadea^a 

 Zthe ba of the lateral branch may progress through solenostely to the d'Ctyostele o 

 he adult But the ontogenetic history of the sporeling was first traced in Alsophlac^..Isa 

 by Gwy n^Vaughan Cauu. of Bo, xvii, p. 709), and illustrated by adiagrammatic drawing 



