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 
Fic. 468. — Hugo De Vries, whose method, but since Darwin’s time 
mutation theory is one of the most the experimental method has 
important contributions to the study },40n especially emphasized with 
of evolution since Darwin’s time. He : . 
has also made valuable contributions the result that rapid strides 
to our knowledge of osmosis. 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 
