de Fraine .— The Seedling Structure of certain Cactaceae. 135 
The seed-leaves possess one median and six or seven lateral bundles, 
which either fuse or end blindly in the tissues of the mesophyll. At the 
base of the cotyledon only one bundle remains, which, at this 
level, has bifurcated and rotated (Diagram 4, Fig. 1). Six epi- 
cotyledonary bundles (e) also enter the hypocotyl; they arrange 
themselves in two groups between the cotyledonary bundles, 
and a cambium soon connects them with the phloem of the 
seed-leaf-traces; no xylem is differentiated in them during 
any part of their course. The xylem of each cotyledonary 
strand soon begins to send off a branch towards the centre 
of the axis (Diagram 4, Fig. 2); this strand almost immediately 
loses its metaxylem, and then branches right and left; at 
a later stage, the adjacent arms from the two cotyledonary 
bundles fuse (Diagram 4, Fig. 3). During these movements of 
the xylem, the phloem-strands lying next to the cotyledonary 
phloem groups fuse with them, and the differentiation of the 
median epicotyledonary phloem-bundle ceases. Metaxylem 
tracheides develop centripetally and a typical tetrarch structure is attained. 
Fig. 6 . 
Nopalea. 
x 1. 
Diagram 4. Nopalea . 
