140 de Fraine.—The Seedling Structure of certain Cactaceae . 
The larger cotyledon (c 2 ) had two strands which rotated and behaved 
as the 4 double ’ bundle of the smaller cotyledon (c v Diagram 6, Fig. i). 
Fusion of the cotyledonary bud-bundle with the seed-leaf-trace took place 
as in C. tortuosus (t v t 2 , Diagram 6, Figs. 2 and 3), and subsequent move¬ 
ments of the vascular elements resulted in a root structure similar to that 
described above for that genus. Towards the base of the root, however, 
changes take place, which result in the formation of a pentarch structure 
(Diagram 6, Figs. 4 and 5). The protoxylem group (x. 2 ) sends off a branch, 
Diagram 6. Cevens peruvianus. 
consisting of a few elements, between the adjacent phloem groups to its 
left ; very soon a phloem strand (gk 5 ) arises to the left of this last formed 
xylem-bundle ; no cambium was present, and the phloem arose by the 
meristematic activity of the cells in this region. At a still lower level the 
protoxylem (xi) branches to the right and to the left, and in this way 
a pentarch root is produced. 
The variation just described, taken in connexion with the somewhat 
similar case figured for C. tortuosus (Diagram 5, Fig. 3), appears to indicate 
the manner in which the simple transition from stem- to root-structure in 
the genus Cereus may have been brought about. A suppression of one 
xylem branch of each cotyledonary bundle, followed by a total oblitera- 
