438 Ganong . — The Comparative Morphology of 
supposition of a specific ‘ bildungs-stoff ’ for the epicotyl, but 
speaks rather for a large power of individual adjustment in 
the protoplasm of the embryo. The phenomenon is, of course, 
well known in other cases 1 , and is, I suppose, comparable with 
the effects of castration in animals. 
The Form-Factors of the Embryos. 
If we view now the forms or shapes of the embryos at the 
stage when germination is completed, and the epicotyl is 
about to appear, we find an immense range of form from the 
very un-Cactus-like Pereskia (Fig. 1) on the one hand to the 
nearly globular, almost cotyledonless Mamillaria (Fig. 47) on 
the other. As this subject constitutes the most important 
part of our present inquiry, I must here treat it in some 
detail, and shall take up the genera in succession. At the 
same time I shall describe the development of the epicotyl 
when it is noteworthy, and add remarks upon other features 
of importance. In addition to references to figures accom- 
panying this paper, I shall mention all other figures of 
germinated embryos known to me, excepting a very few 
which are worthless, so that in this respect I mean this work 
to be monographic. Finally, I shall add a summary of what 
may be deduced as to form-factors. 
1. Genus Pereskia. 
P. aculeata , Mill. Figure 1. 
P. Piiitache, Karw. Figure 9, PI. II, in Zuccarini. 
P. Bleo, DC. Figure (embryo in seed), PI. LX II I in Schumann, Flora brasiliensis. 
This genus consists of climbing woody forms with perfectly 
developed leaves, merging over to upright succulent species, 
approaching and perhaps merging with Cylindropuntiae. The 
embryo (Fig. 1) of P. aculeata has thin, very leafy cotyledons, 
showing distinct netted veins ; their asymmetry is due to 
their position in the seeds, which are very flat. As they 
grow they become jointed at the base, precisely as are 
1 Jost, Prings. Jahrb. 1895 ; also very easy to produce in young Bean-plants. 
