the Embryos and Seedlings of the Cactaceae. 447 
This genus, which merges with Cereus through the climbing 
triangular species (like C. triangularis\ contains mostly epi- 
phytic forms in which the ribs are reduced to two, resulting 
in flat phyllocladia (with axillary buds only upon the margins), 
which finally become thin and leaf-like upon cylindrical stems. 
These phyllocladia are set vertically, which probably comes 
about through suppression of the lateral ribs. Goebel has 
given a full account of the form-conditions in this genus. 
The germinated embryos show a close resemblance to those 
of the climbing Cerei. In P. angtdiger and P. Ackermanni 
(Figs. 1 8, 19), however, the cotyledons are somewhat less 
leaf-like than in P. phyllanthoides grandiflorus and P. Phyll- 
anthus (Figs. 20, 21). In the latter the cotyledons are even 
more leaf-like than in any of the climbing Cerei, and show 
distinctly a yet greater departure from the triangular towards 
a rounded outline. This enlargement and rounding is, of 
course, in adaptation to the more mesophytic conditions which 
surround them. They are all of a clear green colour. 
The epicotyls of the different species I have studied show 
considerable differences. Thus in P. anguliger four or five 
ribs form nearly at once, showing clearly enough the nearness 
of this species to Cereus ; indeed the early stages of the 
seedlings are very Cereus-Yike. The same is true of P. phyll- 
anthoides grandiflorus , and, according to Goebels figure 
(Plate II, Fig. 6), of P. latifrons . But I think Goebel's figure 
does not represent this species, but some Cereus. P. latifrons 
has very flat broad phyllocladia and belongs near stenopetalus ; 
indeed Schumann considers it probable that latifrons and 
stenopetalus are identical. But Goebels own figure for steno- 
petalus (p. 104) is entirely different, and exactly what is to 
be expected for both stenopetalus and latifrons. P. Phyllan - 
thus , which has the most leaf-like cotyledons of all, has an 
epicotyl of special interest (Fig. 21). The two first leaves 
form at right angles to the cotyledons, and the next two over 
the cotyledons ; but the fifth comes over the third or fourth, 
not over the first or second, so that the epicotyl becomes 
at once two-ribbed and flat, and this flattening is in the plane 
