482 Introduction to the Study of Science 



new varieties. He discarded all of the hybrids except a very 

 few that had extra large fine flowers. These, however, had in 

 his judgment one defect : they were not pure white as he desired 

 them to be. He learned that in Japan is grown a rather small, 

 but pure white daisy. Obtaining some of the seed of this 

 plant, he combined it by cross-fertilization with the new large 

 variety which he had originated. He desired to produce in 

 a single plant the two sets of characters, that is, the large size 

 and the pure white. He succeeded, and named the product 

 the Shasta daisy. 



Many new fruits and vegetables have been similarly produced 

 by his labors and genius. The Burbank potato is known every- 

 where. The plumcot is now found in the general market, 

 a product obtained by combining the apricot and the plum. 

 He improved the peach and the plum as to size and quality. 

 One of his late creations is the spineless cactus, which is expected 

 to prove of great value, because it is excellent food for cattle 

 and it produces a fruit said to be of pleasing flavor and of use 

 as food for man. 



SUMMARY 



Comparatively few seeds produced grow to mature plants and re- 

 produce their kind. 



Selection in nature depends upon the following : prodigality of 

 nature, individual variation from the general kind, relation of varia- 

 tions to environmental conditions or fitness, and heredity. 



By natural selection new species are slowly evolved. By artificial 

 selection man controls and hastens the production of new varieties 

 and species. 



The work of Luther Burbank is an example of the value of artificial 

 selection. Some of his achievements are the blue poppy, the fragrant 

 calla lily, the Shasta daisy, the Burbank potato, the plumcot, and the 

 spineless cactus. 



REVIEW QUESTIONS 



1. Why is it necessary for man to cultivate plants? 2. What are 

 the conditions that make it impossible for all plants that start growth 

 to reach maturity? 3. What are the conditions that a plant must 



