452 Ganong . — The Comparative Morphology of 
io. Genus Hhipsalis. 
R. Cassytha, Gaertn. Figure 31 ; also in Irmisch, Botanische Zeitung, 1876; 
also Pfeiffer, Fig. 13, PI. XV. 
R. ( Lepismium ) commune , Pfeiff. Figure in Goebel, PL II, Figs. 3 and 4 
(misnamed Z. radicans in explanations; see p. 102 of text) ; also Pfeiffer, PL XVI, 
Fig. 12. 
This very important genus has been fully discussed in 
a well-known memoir by Vochting 1 (which curiously neglects 
the early stages), and more briefly by Goebel. All of the 
species are small and epiphytic, with joints sometimes ribbed, 
sometimes cylindrical, sometimes flat. They • are, without 
doubt, derived from slender climbing Cerei. I have been 
able to study embryos only of the well-known R. Cassytha , 
and figures of no others are in the books, but Goebel has 
given a very satisfactory account of five other species which 
he has studied (pp. 103, 103). R. Cassytha in its embryo and 
seedling stages has been exhaustively described and figured 
by Irmisch in his ‘ Ueber die Keimpflanzen von Rhipsalis 
Cassytha 
In R. Cassytha the cotyledons are as broad as the hypocotyl, 
thus recalling Cereus , but they are stouter than in that genus 
and more nearly round than flat in section, and merge more 
evenly into the hypocotyl. The latter is also proportionally 
longer than in Cereus (Fig. 31). They are clear green in 
colour. From the epiphytic, and therefore to some extent 
mesophytic, habit of this genus, one would expect more leafy 
cotyledons ; but perhaps, as suggested for Epiphyllum , the 
xerophytic outweigh the mesophytic influences in the epi- 
phytic life. The figure given by Pfeiffer suggests very much 
more leaf-like cotyledons than do Goebel’s figures, and it is 
difficult to believe they represent the same species. 
In R. Cassytha the epicotyl contains at first four distinct 
ribs, which merge above into the spirally-placed clusters 
characteristic of this species. In this we have another good 
illustration of biogenesis ; the ribs are no doubt an inheritance 
In Pringsheim’s lahrbiicher, IX. 
