HOW THE MAMMALS DEVELOPED Ig5 
and the offspring are as nearly as may be like the 
parent from which they arose. 
The gardener who wishes to obtain new varieties 
is not content with this method. If he plant the seed 
of the potato the outcome will be most uncertain. His 
seed must be taken, of course, from the fruit of the 
potato, and most of these plants never fruit. Every 
grower of large quantities of potatoes will have no- 
ticed occasionally, on the tops of the plant, after the 
flowers disappear, a globular growth looking not un- 
like a small tomato, but with a tendency to become 
purplish green in color. This is the fruit of the 
potato and in it are the seeds. When these are planted 
all sorts of potatoes are liable to start up. Most of 
them will prove worthless. An occasional seed may 
produce an uncommonly fine plant. This new variety 
may thereafter be propagated from the tuber, as the 
potato itself is called, and the new strain will be kept 
constant in this way. This method of using the seed 
for reproducing the plant is called the sexual method, 
because two parents cooperate in the production of 
the seed. The pollen came from one parent and the 
ovule, which after fertilization swelled up into the 
seed, came from another. By this combination of 
two individuals new varieties become quite possible. 
Nature seems to be more concerned in improving her 
strain than in maintaining her older strains. In all 
