36 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
assistance? That variation does issue a new species, and that natural 
selection is a factor, though not the only factor, in determining results, 
is, in my opinion, as certain as that grass grows although we cannot 
seeit grow. Furthermore, I believe I have found indubitable evidence 
of species-forming variation advancing in a definite direction (ortho- 
genesis), and likewise of variations in various directions (amphi- 
genesis). If I am not mistaken in this, the reconciliation for natural 
selection, and orthogenesis is at hand.” 
In concluding this brief account of orthogenesis, it should be said 
that definitely directed evolution is now believed to be one of the laws 
of organic evolution, but that we have no clear ideas as yet as to what 
are its underlying causes. Therefore orthogenesis is not @ causo- 
mechanical theory of evolution at all. 
MUTATION OR HETEROGENESIS THEORIES 
The theory of “mutations” is associated with the name of Hugo 
De Vries, the well-known Dutch botanist; that of “heterogenesis,”’ 
with the name of H. Korchinsky, a Russian. 
Though Korchinsky anticipated De Vries by several years, his 
work was not supported by the large amount of experimental data 
that characterized that of the great Dutch worker. The relative 
claims for recognition as the founder of the mutation theory are 
almost on a par with those of Darwin and Wallace for the natural- 
selection theory. Both Darwin and De Vries held back their theo- 
ries until they appeared to be adequately supported by personally 
collected facts. 
There is a striking parallelism between the ideas and conclusions 
of De Vries and those of Korchinsky, and since this is true a résumé of 
De Vries’s better-known work will serve to give the essentials of the 
whole conception. 
De Vries began his genetic experiments by a study of the variations 
of plants in the field. After learning their normal variability in 
nature, he transferred them to the experimental garden and there 
attempted to improve them by selection. He found that the improved 
living conditions due to better soil and cultivation induced a wider 
range of variability in size, luxuriance,and fecundity. Such variations 
were plus or minus in their character, fluctuating about a mean or 
average. It was exactly this type of variability that Darwin empha- 
sized as the raw material of evolution; but De Vries found by experi- 
ment that selection had no permanent hereditary effect when based 
