142 de Froine .— The Seedling Structure of certain Cactaceae. 
the bast takes place until it occupies the position characteristic of the Cereus 
root-structure, and with these movements the transition is completed. In 
this series and in all the seedlings of Pilocereus examined, only protoxylem 
was present at the stage observed. 
Series 2. In this seedling, towards the base of the cotyledon, four 
small vascular strands were present, but at the cotyledonary node the 
number was reduced to one. This bundle soon bifurcated, the tubercle- 
bundle fused laterally with one half of it, and the remainder of the transition 
followed the course described for Series 1. 
Rhipsalis. 
Fig. 9. 
Rhipsalis 
dissimilis. 
x if 
Seeds belonging to two species only of this genus germinated. The 
seedlings were very small and resembled those of the genus 
Mamillaria in the possession of a globular hypocotyl ; they 
differed, however, in owning two minute pointed cotyledons. 
The cuticle was much more strongly developed in these seed¬ 
lings than in those of any other genus, but in other respects 
the general characteristics of the cotyledons and hypocotyl 
are those of such a group as Echinopsis. 
Rhipsalis Warmingiana, K. Schum. One small endarch 
bundle passes into the hypocotyl from each cotyledon, but 
during its inward passage bifurcation of the phloem takes 
place; at this stage, and indeed throughout the whole length 
of the hypocotyl, only protoxylem is present. Rotation of the phloem 
groups follows immediately on their bifurcation, and the movement con¬ 
tinues round the stationary protoxylem, until they lie at right angles 
to their former position. A general centripetal displacement of all the 
vascular elements follows until the opposite groups of phloem lie close 
together, when fusion of them takes place. New xylem elements develop 
centripetally to the protoxylem until a central plate is formed ; thus the 
diarch root-structure is arrived at. 
Rhipsalis dissimilis , K. Schum. The seedlings of this species are very 
similar to those of R. Warmingiana, but the stem apex is rather more 
depressed, giving rise to a short cotyledonary tube. Further, bifurcation 
of the phloem takes place at the base of the cotyledons, and is not delayed 
until the hypocotyl has been entered, as in the former species. 
Echinocereus. 
The seedlings of the species of Echinocereus examined show a fairly 
close resemblance to those of Cereus , but there is a slight diminution both 
in the length of the cotyledons and of the hypocotyl, and the latter is rather 
more globular than in any of the species of Cereus. The epidermal cells 
of the cotyledons are elongated and almost pointed ; but there is no 
differentiation of these cells as is the case in some of the Cerei. 
