de Frciine .— The Seedling Structure of certain Cactaceae . 149 
Transition. 
A. Species in which the vascidar symmetry of the root is attained by 
the cotyledonary bundles only. 
Echinopsis Eyriesii , Pfeiff. and Otto. Each cotyledon supplies the 
hypocotyl with one endarch collateral bundle, approximately equal in size 
to a single mesophyll cell. Soon after entering the node the phloem 
bifurcates, and its two halves rotate until they lie almost in a straight line 
with the protoxylem; no metaxylem is present. The four strands thus 
produced show no further change beyond a slight centripetal displacement, 
and the root structure is of the typical Cereus type (Fig. 11). 
Echinopsis Zuccarinii , Pfeiff. and Otto. These seedlings differ from 
those of E. Eyriesii in but one respect; in one series the root-structure 
gives place towards the root-tip to a completely diarch arrangement by the 
fusion of the opposing groups of phloem. 
Echinopsis oxygona , Pfeiff. and Otto. In this species the bifurcation 
of the phloem in the cotyledonary bundles takes place before the node is 
reached ; in other respects the transition-phenomena resemble those of 
E. Eyriesii. The Cereus type of root is not maintained, however, for just 
as differentiation is about to cease the opposing phloem groups fuse, giving 
rise to a diarch root. 
B. Species in which the vascidar symmetry of the root is attained by 
means of tubercle and cotyledonary bundles. 
The upper region of the hypocotyl in all the seedlings examined 
showed two vascular strands, in which the phloem groups appeared on 
either side of a centrally placed group of protoxylem elements, which often 
