de Frciine.—The Seedling Structure of certain Cactaceae. 127 
seed-leaves, is a characteristic feature of the Cactaceae, and may be 
due to the shape of the seed. The embryo is curved, and has a small 
quantity of endosperm lying against its concave side ; the smaller cotyledon 
is on this side and is covered by the larger convex one. The seed-leaves 
have no true petiole, but towards their base they are narrowed off, and are 
almost oval in transverse section. Each cotyledon has, in its broadest part, 
from eleven to twelve small vascular strands ; these either fuse among them¬ 
selves or end blindly in the mesophyll, until towards the base of the seed- 
leaf only the median and two lateral bundles remain. Fairly high up in 
the seed-leaf the median bundle bifurcates, and the phloem groups rotate 
until they lie almost in line with the xylem, in which by this time the 
protoxylem has become exarch. The two lateral bundles (/) fuse with the 
bifurcated main bundle towards the base of the cotyledon in the manner 
indicated in Diagram 1, Fig. 1. 
Diagram i. Pereskia n. sp. In this, and in all the following diagrams, the protoxylem is 
indicated by the black areas, the metaxylem by dots, the phloem by diagonal shading, and the 
cambium by a broken line. 
The xylem elements are much scattered, and it is extremely difficult 
to make out the position of the protoxylem with any degree of certainty, 
but it is highly probable that during the passage into the hypocotyl the 
protoxylem branches in three directions (Diagram 1, Fig. 2). At this stage 
