130 de Fraine .— The Seedling Structure of certain Cactaceae. 
Almost immediately after the entry into the hypocotyl has been made 
the protoxylem branches in three directions ( a , b, c, and a v b v c v in 
Diagram 2, Fig. 2, and Fig. 3, B), the adjacent arms (b, b v and c , c 2 ) fuse and 
give rise to the two intercotyledonary poles of the tetrarch root (Diagram 2, 
Fig. 4 a. Opuntia Tuna. Series B. x 220. 
Fig. 3). In this species, and in other of the Opuntias, there is thus the 
formation of a tetrarch root-structure from two cotyledonary traces by 
means of a transition which is of a type practically identical with 
Anemarrhena} a type which, so far as it has been possible to ascertain, has 
1 Sargant, E. : loc. cit. 
