480 Introduction to the Study of Science 



fifty more, and this continued without interference, dandelions 

 would soon possess the earth. But other plants, birds, insects, 

 and plant diseases destroy enormous numbers of seeds and 

 plants, so that the number remains on the whole about the 

 same. 



Variations. The second of the conditions is that among 

 the large numbers of offspring there are practically countless 

 variations from the general kind. No two individuals are alike 

 in all respects. This may be verified by examination of any 

 number of plants grown in uniform conditions from seed selected 

 of apparently equal quality, size, and weight, and from an- 

 cestors of the same degree of excellence. 



Adaptation. In the third place, it is altogether probable 

 that among the numerous variations some will be well adapted 

 to the environmental conditions, and will therefore be able to 

 survive in the struggle and propagate their kind. In your 

 studies of plants, look for such growing wild and in cultivated 

 lands. 



Heredity. The fourth condition is that the successful 

 in the struggle transmit by heredity to their offspring the 

 qualities that made them the fittest of their kind and insured 

 their survival. In this manner through slight variations of 

 individuals from their kind, transmitted and accumulated from 

 generation to generation, the new varieties may eventually 

 form what the botanist would call new species or races. These 

 species, like the individual ancestors, are the fittest to survive 

 because they are adapted to their environment or are able suc- 

 cessfully to resist adverse conditions. 



228. Artificial selection. By natural selection new species 

 of plants have been evolved slowly. This is the method of 

 nature, operative long before the appearance of man. By the 

 study of plants and animals man has acquired a knowledge 

 of nature's ways and has applied this knowledge to the develop- 

 ment of new varieties or species at a more rapid rate than seemed 

 possible with the undirected forces of nature. 



