270 BOTANICAL GAZETTE [APRIL 
megaspore mother cells, a large number of which begin to appear 
only to degenerate when one of them is selected and enlarges to 
form the single tetrad of megaspores. This selection is neither 
embryonic, gametic, nor gametophytic, but belongs to a distinct 
category, somewhat similar to some other types of developmental 
selection which will be discussed later. 
Developmental selection among spermatophytes 
EMBRYONIC SELECTION.—Most striking of the forms of develop- 
mental selection of seed plants is the embryonic selection illustrated 
by the polyembryony of gymnosperms, which has already been 
described in a general way. The several embryos originating from 
the fertilized eggs engage in a competition in which the most 
vigorous individual is always the winner. Not only must the 
embryo rapidly become massive and multicellular, but it must also 
produce a stiffer and more vigorous suspensor, one which keeps 
the successful embryo in the commanding position. The winner 
is usually the foremost of the group of embryos, where the embry- 
onal tubes of the elongating secondary suspensor are able to push 
the other competitors back, away from the most favorable position. 
This applies whether cleavage polyembryony occurs or not. The 
mature conifer seed has a single large embryo, but the remains of 
some of the other embryos participating in the competition can 
usually be found, crushed against the archegonial end of the 
embryonal cavity within the gametophyte (endosperm) by the 
suspensor or radical end of the successful embryo. 
TIC SELECTION.—Another type of developmental 
selection is gametophytic selection. This is not intended to apply 
to the form of natural selection occurring between independent 
gametophytes, as those of liverworts or ferns, in the external 
environment, but rather to a plurality of male or female gameto- 
phytes which are dependent on a sporophyte, as they are in seed 
plants. It is well illustrated by the pollen tubes of a pine or other 
conifer whose competition predetermines in a measure which of 
the several archegonia shall first be fertilized. Although fertiliza- 
tion in conifers is almost simultaneous even in the various cones of 
the same tree, a fact first pointed out by HormersTErR (21), this 
