de Fraine .— The Seedling Structure of certain Cactaceae. 153 
of each cotyledonary bundle bifurcates and rotates round the xylem, which 
consists only of protoxylem tracheides; as soon as this is completed the 
epicotyledonary strands, which have been moving outwards, fuse with 
the cotyledonary bundles. This Cereus arrangement persists almost to 
the apex of the root, but finally the phloems fuse and a diarch root 
results. 
E. tricolor , Series 2, shows a slight difference from the above in its 
possession of a cotyledonary bud-bundle, in addition to the six epicotyle¬ 
donary strands. These bud-bundles and t 2 , Diagram 10, Fig. 1) pass 
obliquely to one side and fuse with one of the epicotyledonary bundles, the 
remaining two strands (e) also fuse (Diagram 10, Fig. 1). The four strands 
thus produced (tj + e, e, t 2 + e, and e, Diagram 10, Fig. 2) move outwards 
and join on to the cotyledonary strands, which have by this time bifurcated. 
The remaining details of the transition are essentially similar to those of 
the other seedlings of the genus. 
Echinocactus Ottonis , Link and Otto. The seedlings of this species 
differ very considerably from those of the other members of the genus in 
their possession of well-marked cotyledonary tubercles, which far surpass 
in importance the seed-leaves themselves, for the latter are reduced to 
mere papillae. This increasing importance of the tubercle over the 
cotyledon is shown in the behaviour of the vascular strands. In all 
the seedlings examined, the tubercle-traces (t v t 2 , Diagram 11, Fig. 1) 
appeared some time before those which supplied the cotyledons, but this 
would naturally be expected from the greater comparative development of 
the tubercle. 
Echinocactus Ottonis , Series 3, illustrates the simplest course of events. 
In its larger cotyledon the two traces (c^t^ Diagram 11, Fig. 2) rotate and 
fuse, thus producing one bundle, as in Echinopsis multiplex , Series 2; in 
the smaller seed-leaf the cotyledonary strand c., remains in situ while the 
