524 



EVOLUTION 



Experimental Evolution 



The early students of science studied plants and animals 

 simply by observing them in the field. They made no effort to 

 control the conditions under which the plants or animals were 

 growing. But one can see that, in order to draw definite con- 

 clusions in regard to the inheritable factors in plants, the ances- 

 try of the plants must be known, their pollination controlled so 

 as to know definitely the parents of the progeny, and the various 

 factors that affect the growth of the plants must be taken into 



account. Likewise, in the study 

 of animals in reference to prob- 

 lems of evolution it is essen- 

 tial to control their breeding 

 and often the conditions to 

 which they are exposed. The 

 early scientists had poorly 

 equipped laboratories or none at 

 all, and science then was chiefly 

 a description of nature and was 

 called "Natural History." 

 Darwin and a few of his con- 

 temporaries put considerable 

 emphasis on the experimental 

 method, but since Darwin's time 

 the experimental method has 

 been especially emphasized with 

 the result that rapid strides 

 have been made in interpreting 

 and explaining facts. 



Hugo De Vries. Hugo De Vries (Fig. 468), director of the 

 Botanic Garden in Amsterdam, Holland, was among the first 

 to apply the experimental method to the study of evolution. 

 Starting with seed selected from plants which he thought were 

 pure, that is, not mixed with another variety, he grew a large 

 number of generations, which, by carefully preventing cross- 

 pollination, were kept pure to the parent type. In order to 

 make accurate comparisons and thereby detect variations from 

 the parents, such as the dropping of parental characters or the 

 taking on of new ones, he not only kept careful records but also 



FIG. 468. Hugo De Vries, whose 

 mutation theory is one of the most 

 important contributions to the study 

 of evolution since Darwin's time. He 

 has also made valuable contributions 

 to our knowledge of osmosis. 



