SEED PLANTS 171 
been found in the higher Conifera, and it is not likely 
that in these spermatozoids exist. 
The development of the embryo in the Conifers shows 
a good deal of difference in different genera. Some- 
times but a single embryo arises from each egg-cell, as 
in most other plants; but sometimes, for instance in the 
common pines and firs, each egg gives rise to a group 
of (usually four) embryos, and the ripe seed may contain 
more than one young sporophyte. Generally, however, 
one of the growing embryos crowds out the others, and 
only this one matures. As in Selaginella and the lower 
Gymnosperms, a long suspensor (Fig. 42, J, sus) is 
formed from the upper part of the egg, while the lower 
portion only gives rise to the embryo itself. By the 
rapid lengthening of the suspensor the growing embryo 
is pushed down into the tissue of the gametophyte, 
whose cells become gradually filled with nutrient sub- 
stances upon which the developing embryo feeds. These 
are not all consumed, however, but a considerable part 
persists in the ripe seed as the “endosperm,” in which 
the young sporophyte is imbedded, and upon which it 
draws for nourishment in the early stages of the germi- 
nation of the seed. The young sporophyte within the 
ripe seed already has all its primary organs developed. 
The stem is prolonged downward into the primary root, 
which is directed toward the opening in the integument 
(nicropyle), while the upper end of the embryo termi- 
nates in the conical stem-apex about which is arranged 
a circle of primary leaves, or cotyledons, ranging in 
number from two to half a dozen or more. 
The ripe seed has a hard, usually dark-colored coat, 
effectually protecting the delicate inner tissues; some- 
