de Frame. The Seedling Structure of certain Cactaceae. 151 
which fuse with the well developed tubercle at the cotyledonary node 
(Fig. 14). A small cotyledonary bud is developed in E. denudatus and 
E. bicolor , which in one seedling of the latter species possesses a vascular 
bundle ; E. hexaedrophorus and E. Wislezeni show no sign of this structure. 
Fig. 14. Echinocactus Ottonis. Base of cotyledon Fig. 15. Echinocactus Ottonis . Cotyledon- 
and its tubercle, b = base of spine group, x 109. and tubercle-bundles, x 109. 
Transition. 
Echinocactus hexaedrophorus , Lem. Each cotyledon supplies the 
hypocotyl with one small endarch bundle, in which the phloem bifurcates 
during the passage through the cortex ; protoxylem only is present in the 
bundles and the phloem groups move round this as round a pivot, until 
they lie one on either side of it. About the central region of the hypocotyl 
new xylem elements arise between the two protoxylem groups until the 
two become connected ; this diarch plate, however, does not long persist, 
for new tracheides arise to the right and left of its central region until 
a cross-shaped xylem mass results. Towards the base of the hypocotyl 
the central elements of the cross disappear and leave four xylem groups 
alternating with the four phloem-bundles of a tetrarch root. 
Echinocactus Wislezeni , Engelm. The bifurcation of the single bundle 
of the cotyledons in this species takes place in the cotyledon. The phloem, 
accompanied by a small quantity of metaxylem, rotates and separates from 
the protoxylem, which it thus leaves exposed in the exarch position. Four 
