REPRODUCTIVE ORGANS 
111 
of the moss-plants is still more true 
of the fern-plants ; while among 
the seed-plants certain spores (pol- 
len grains) are conspicuous (see 
Fig. 110), but the eggs can be ob- 
served only by special manipulation 
in the laboratory. Seeds are neither 
spores nor eggs, but peculiar repro- 
ductive bodies which the hidden 
egg has helped to produce. 
73. Germination. Spores and 
eggs are expected to germinate ; 
that is, to begin the development 
of a new plant. This germination 
needs certain external conditions, 
prominent among which are defi- 
nite amounts of heat, moisture, 
and oxygen, and sometimes light. 
Conditions of germination may be 
observed most easily in connection 
with seeds. It must be understood, 
however, that what is called the 
germination of seeds is something 
very different from the germination 
of spores and eggs. In the latter 
cases, germination includes the very 
beginnings of the young plant. In 
the case of a seed, germination begun 
by an egg has been checked, and 
seed germination is its renewal. In 
other words, an egg has germinated 
and produced a young plant called 
the "embryo," and the germination 
of the seed simply consists in the 
continued growth and the escape of 
this embryo. 
FIG. 108. A portion of the 
body of a common alga 
( (Edogonium), showing 
gametes of very unequal size 
and activity ; a very large 
one (o) is lying in a globular 
cell, and a very small one is 
entering the cell, another 
similar one (s) being just 
outside. The two small 
gametes have hair-like pro- 
cesses and can swim freely. 
The small and large gam- 
etes unite and form an egg. 
c 
FIG. 109. A group of swim- 
ming cells : A, a spore of 
(Edogonlum (an alga) ; 
B, spores of Utothrix (an 
alga) ; C, a gamete of 
Equisetum (horse-tail or 
scouring rush). 
