de Fraine .— The Seedling Structure of certain Cactaceae. 129 
developed than in Pereskia n . sp. ; and there is throughout the whole 
seedling a great abundance of cluster crystals. 
Opuntia. 
In external features the seedlings of this genus still maintain an almost 
normal dicotyledonous appearance (Fig. 2), but the hypocotyl has become 
somewhat more reduced in length as compared with 
Pereskia , while, at the same time, it is slightly more suc¬ 
culent, and the cotyledons though still leafy are distinctly 
more fleshy. The seed-leaves, as in the other genera, are 
markedly asymmetrical; they have a network of veins, as 
many as ten vascular strands being present in the transverse 
section of the cotyledon at some levels, but towards the 
base these are usually reduced to one, in which, by this 
time, bifurcation has generally occurred; there is never 
any suggestion of a petiole to the cotyledon, such as is 2 * Opuntia 
indicated in Pereskia. The large cortical cells of the hypo¬ 
cotyl frequently contain crystals, e. g. O. imbricata and O. Bergeriana , and 
mucilage sacs are a characteristic feature of O. stricta and O. Pseudo-tuna. 
Transition. 
Opuntia Ficus-indica , Mill. In this species one ‘ double’ bundle enters 
the hypocotyl from each seed-leaf; in it the bifurcation and subsequent 
separation of the phloem have proceeded so far that the xylem, which 
is composed of protoxylem elements only, is situated between two groups 
of phloem elements (Fig. 3, a). 
B. \ / 
Fig. 3. Opuntia Ficus-indica. x 220. 
K 
