HOW THE MAMMALS DEVELOPED 195 



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 co.urse, 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 



