EVOLUTION 229 



varieties are so different from the original forms that the two 

 are scarcely recognized as belonging to the same species. For 

 instance, the prickly lettuce, a common weed of waste ground, 

 is the parent of the garden lettuce. The same condition exists 

 with regard to the animals, though plants, being less highly 

 organized and yielding more readily to experiment, probably 

 show the most remarkable results. In producing these 

 forms man has followed nature's methods in selecting those 

 most suited to his purpose. What man considers best, how- 

 ever, may not be the best from nature's standpoint, and are 

 possibly not fitted to survive in a struggle with their environ- 

 ment, but under man's protection this is no obstacle to con- 

 tinued existence. A large number of our cultivated plants 

 must be protected from the weeds by cultivation. Domestic 

 animals must be protected in like manner from their foes. 

 Selection, however, is only one phase of breeding. In plants 

 especially, hybridizing or the union of the sperms and 1 eggs of 

 different species or varieties, is frequently utilized. Sports of 

 all kinds are of value in affording a point from which to begin 

 experiments. In order to induce a species to sport, variations 

 of the food, temperature, and other characteristics of the 

 surroundings are often made. In the early history of breeding 

 the forms to be propagated were selected more or less arbitrar- 

 ily, but with the discovery of Mendel's Law of inheritance, the 

 work of breeding now proceeds upon more scientific lines. 

 Mendel's discovery consists essentially in the recognition of 

 the fact that the gametes eggs and sperms of a pure organ- 

 ism carry only the characteristics of that organism, and when 

 the gametes of two different forms are united, these characters 

 may be rearranged in new combinations with great accuracy. 

 With these facts clearly understood, it becomes possible, by 

 crossing plants or animals in different ways, to obtain rapid 

 improvement in the species selected and thus produce many 

 new and promising forms. 



