456 
Hill and de Fraine. On the 
of a horseshoe-shaped central cylinder enclosing a central mass ot 
parenchyma ; in Dioon edule and Encephalartos Altensteinii of a concentric 
cylinder with a central pith. 
13. The fusion of the cotyledonary traces with one another, or with the 
plumular bundles, or with the central cylinder, does not always take place 
at the same level. 
14. The seed-leaf bundles are not of equal value in the production 
of the root-structure ; some traces play a wholly subordinate part, and the 
behaviour of similarly situated bundles in different individuals of the same 
species varies. Thus in Dioon edule , in one example, the two poles of the 
root-structure situated in the plane of the seed-leaves were organized from the 
three central bundles of one cotyledon, and the two central strands of the 
other seed-leaf ; and the intercotyledonary poles were formed, one from the 
extreme lateral traces on the one side, and from a single lateral bundle on 
the other. In another example the four lateral traces, two from each 
cotyledon, each formed one pole of the root-structure, so that there were 
four intercotyledonary poles in addition to the two situated in the plane of 
the cotyledons. 
In Stangeria it is more difficult to allocate values ; one pole was 
formed chiefly from a lateral strand of one of the seed-leaves, the second 
pole from the other lateral bundle and part of the central trace of the same 
cotyledon, while the third pole was organized chiefly from the vascular 
tissue of one of the two bundles of the other cotyledon. 
In Encephalartos Altensteinii , the central bundle of one cotyledon 
organizes one pole of the root-structure ; the other two poles are formed 
from the two lateral traces of the other seed-leaf. 
15. The poles of the root-structure are formed successively in Stan- 
geria and in Encephalartos Altensteinii. In the case of Dioon edule the 
two poles situated in the plane of the cotyledons are the first to appear, 
those in the intercotyledonary plane being organized at a slightly lower 
level. 
16. In one seedling of Macrozamia spiralis an isolated concentric strand 
of vascular tissue occurs in upper regions of the hypocotyl. 
Root. 
1 7. In Ginkgo an addition of protoxylem elements may occur after 
the root-structure has been attained. 
18. In Stangeria sp. the primary root may dichotomize. 
19. After the initial root-structure has been attained the number ol 
poles may be increased at lower levels ; thus, in Encephalartos Altensteinii , 
the initial structure may be triarch but it becomes tetrarch or pentarch at 
lower levels. 
