de Fraine.—The Seedling Structure of certain Cactaceae. 157 
possesses a vascular strand which traverses its tissue to the base of thespine 
group, but the cotyledon is usually without a vascular supply. In some 
cases a bundle may reach the base of the seed-leaf papilla, but more usually 
it does not do so, but ends blindly in the hypocotyl; the name cotyledonary 
bundle will still be applied to these strands, however, for, from their 
position, they obviously represent the seed-leaf-traces of the other genera. 
The behaviour of the tubercle- and cotyledon-bundles will be described 
later, in the account of the transition-phenomena. 
The still further reduction of the cotyledons shown by M. pentacantha , 
M. hexacantha :, and M. eriacantha is accompanied by the partial suppression 
of the tubercles, which are here represented by cotyledonary buds, such as 
were described as occurring in some species of Cereris ; these buds may 
or may not possess vascular tissue. M. spinosissima and M. Donatii have 
neither tubercles nor buds, and the cotyledonary papillae are almost 
entirely suppressed ; while, finally, M. pusilla has reached the stage in which 
the seedling consists of hypocotyl and root only; cotyledons are entirely 
absent. 
The structural details of the hypocotyl and the root so closely 
resemble those described in Echinopsis that any further account of them is 
quite unnecessary. 
Transition. 
The details of the transition-phenomena in the different species of 
Mamillaria examined differ considerably, so that it is quite impossible to 
give any general description ; for this reason the account of the various 
species will be given separately. 
