ON THE SEXUAL ORGANS OF THE CYCADACEJRX. 91 
embryonic form persists much longer than usual. It is also much 
more complex; for, whilst among Angiosperms the proembryo only 
forms a simple axis, represented sometimes by a single cell, and only 
gives rise to a single bud, a single embryo, a single individual, —the 
proembryo of Gymnosperms divides into branches, and produces, or 
might produce, numerous buds or embryos. It imitates, to some ex- 
tent, the higher sexless form, by its ramification and the production of 
multiplied buds combined into one whole. If we consider the life of 
the generating cells, the microspores and macrospores, as terminating 
at the moment of their mutual union, a view which admits of support, 
there would then be a triple alternation of forms within the limits of 
the individual. But it seems more simple to consider the sexless in- 
dividual of more perfect orgauization as producing by generation, or 
differentiation, into two distinct states, a more simple organism o 
short duration, returning finally to the original form with higher or- 
ganization, and life indefinitely prolonged. 
Among the vascular Cryptogams, alternate generation manifests it- 
self more clearly, because the two forms appear distinctly at the exte- 
rior, whilst among Phanerogams the cellular transitory organism is 
enclosed in a portion of the higher organism. The spores produced by 
the vascular sexless plant develope into organisms simple in structure 
and wholly cellular (prothallium), which produce the generating-cells. 
Among the lower vascular Cryptogams, both sexes originate from the 
same spore; among the higher, from different spores,—the one set 
microspores (male), the other macrospores (female). In both cases, 
however, a new individual results from their union, which possesses 
vascular bundles, is differentiated into stem and leaves, and is destitute 
of sex. Yet here the embryo does not proceed directly from the cen- 
tral cell of the archegonium ; the first product is a proembryo, the ter- 
minal cell of which becomes the embryo. Thus, then, among Phanero- 
gams, the generating-cells occur ou the higher essential form, among the 
Cryptogams on the lower form. 
Hofineister has made the remark that the Conifere (the Gymno- 
sperms) are with respect to the development of the embryo, interme- 
diate between the higher Cryptogams and the Phanerogams. Among 
the Gymnosperms, the embryo-sae soon becomes free and detached 
from the tissues which surround it ; the formation of the endosperm is 
comparable to the production of the prothallium ; the corpuscles are 
