﻿7 6 



VEGETATIVE FEATURES. 



S.2&0.XI0O. 



xylem is exclusively made up of spiral tracheitis. In the more ancient form Cycas, 

 however, scalariform tracheitis are also abundant, and it is very evident from the 

 great variability in the relative amounts of xylem, and proportion of spiral, pitted, 

 and scalariform elements, as seen in isolated sections cut at random, that no very 



'■m^qf+sn yw/woa direc i coinp T sons or 



i k I lUA A \l/Av*Jr- conclusions have yet 



been reached concern- 

 ing tracheidal organ- 

 ization in the Cycada- 

 les, Cycadofilices, and 

 Cordaitales. To yield 

 exact comparisons of 

 value in generic, to say 

 nothing of specific de- 

 terminations, the rela- 

 tive age and develop- 

 ment would have to be 

 known and carefullv 

 oriented sections cut 

 from the several trunk 

 regions found to be rep- 

 resentative through- 

 out a long and varied 

 series of existing and 

 extinct genera. An 

 interesting agreement 

 between the tangential 

 sections of the xylem 

 zone of Cycadeoidea 

 and Cordaites New- 

 bcrryi is illustrated by 

 the accompanying fig- 

 ures 42 and 43. Aside 

 from a difference in the 

 relativesizeof the med- 

 ullary ray cells, a close 

 parallel is afforded. 

 Phloem. 



The parts of the 

 phloem are in reverse 

 alignment to those of 

 the xylem — that is, the 

 phloem rays decrease 

 in width and the cells 







11QB 





Fig. 41 A. — Cycadeoidea Wielandi. 



S.2i,0.T.393.>-loo. 

 S. 260. X 100. Continued from 



/ 



T. 393 

 fig. 40. 



e, Transverse section through the phloem, showing the origin of the phloem of a horse- 



shoe bundle. 100. 



f, Transverse section through xylem showing a part of the origin of the xylem of one of 



the bundles passing out from the woody cylinder into the cortex. X 100. The 

 innermost obliquely set cells have sub-hexagonal pittings in their walls. Further 

 out the initial bundle cells present more and more cribriform and finally scalari- 

 form patterns. 



