254 BOTANICAL GAZETTE [APRIL 
embryo develops is much later in its origin, and is usually very soft 
and gelatinous in these early stages. This and the reduced sus- 
pensor of angiosperms may largely account for the fact that angio- 
sperm polyembryony does not usually result in the definite selection 
of a single embryo before the seed is shed. 
Brown (1), who discovered polyembryony,. pointed out that 
plurality of archegonia makes possible the fact of polyembryony 
among both cycads and conifers. It has been found also (5, 35) 
that in some conifers the zygote may undergo cleavage, resulting 
in several young embryos which compete with each other. Thus 
the fertilization of only one egg in Pinus, for example, results in 
the formation of eight embryos by cleavage (cleavage poly- 
embryony), only one of which survives and completes its term of 
development (figs. 1-6). In other conifers, as in the spruce, the 
egg gives rise to only one embryo, but in any event the plurality of 
eggs makes possible simple polyembryony, in which a selection of 
embryos occurs. 
A scheme of phylogeny, based in part on the character of 
polyembryony, whether simple or by cleavage, has been outlined 
in previous papers (5, 6). All the facts at hand seem to indicate 
that practically all conifers which do not possess cleavage poly- 
embryony show structural evidence of having passed through this 
condition in their phylogeny. This indicates that either cleavage 
polyembryony originated among ferns, or it originated during the 
transition to the seed habit. All evidence is in favor of the latter 
alternative, and a definite hypothesis to account for the origin of 
cleavage polyembryony will be outlined in a later paper. In 
general, cleavage polyembryony is well developed among the more 
primitive conifers, and was eliminated sooner or later in all but one 
or two phyletic lines. Whether cycads passed through a similar 
stage of cleavage polyembryony is very uncertain. Nothing in 
the embryogeny of cycads thus far described appears to suggest this, 
but their simple polyembryony is doubtless of the same fern origin 
as that of conifers, that is, plurality of archegonia in the ferns 
from which cycads were derived. 
Embryonic selection, either through cleavage polyembryony, 
plurality of archegonia, or a combination of both, is practically 
