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outcroppings of evolutionary ideas. On the botanical side, the views 
of Dean Herbert and of Naudin were based largely upon experimenta- 
tion rather than speculation and were expressed with especial clearness. 
The former (1822 and 1837) said that "horticultural experiments have 
established beyond the possibility of refutation, that botanical species 
are only a higher and more permanent class of varieties." The latter 
(1852) said that the methods by which the gardener produces new 
varieties coincide with the processes by which new species originate 
in nature. It remained for Darwin, however, to refute finally the 
doctrine of special creation. 
Darwin ascribed the origin of new species in nature to the natural 
selection of favorable variations. With this view, in its most general 
aspect, nearly everyone is in accord. But the great problem of 
evolution still remains, — what is the source of the variations which are 
selected? Darwin could not answer this problem satisfactorily because 
no one had yet discovered the distinction between fluctuating varia- 
tions, which are not inherited, and mutations, or germinal variations, 
which are inherited. He also went astray, as we now think, in be- 
lieving that the effect of use or disuse of an organ could in some way 
impress itself upon the germ-plasm and become hereditary. The few 
who still hold that the selection of continuous variations would suffice 
to bring about specific differentiation can bring forward little or no 
evidence to support their view. The evidence all points to the utmost 
fixity of organisms, aside from mutations. In order not to perpetuate 
a misrepresentation of Darwin's views which he himself particularly 
resented, it should be said that, after the publication of the Origin of 
Species, Darwin came to believe that he had formerly underrated the 
value of mutations ("spontaneous variations") in bringing about 
diversity. Even in the first edition of his great work he stated his 
belief that the selection of insensible derivations had not been the 
exclusive means of modification. Darwin's caution, however, was 
not shared by all of his followers. Exaggeration and misrepresentation 
of his views led to an almost universal conviction that modification 
was too slow a process to be made the subject of experimental inquiry. 
Thus it came about that the Origin of Species was followed by a period 
of stagnation, as far as experimentation was concerned. 
During this period there were indeed a few experimenters, with the 
courage of their convictions, who carried on genetical studies. One of 
them was Mendel, whose investigations aroused no interest among 
