HISTORICAL ACCOUNT OF EVOLUTION THEORY 37 
to fluctuating variations, since the latter were merely somatic responses 
on variable growth conditions. This negative finding led him to 
renewed interest in discontinuous or saltatory variations as the only 
alternative to fluctuating or continuous variations. 
He looked far and wide among species of wild plants for a species 
that might exhibit a significant amount of saltatory variation and 
finally discovered in the evening primrose (Oenothera lamarckiana) 
what seemed to exhibit exactly the hoped-for characteristics. This 
large, stately plant with conspicuous yellow blooms had escaped from 
cultivation and was growing wild in the fields. In addition to a large 
number of plants that showed only minor differences among them- 
selves, De Vries found several individuals growing among the typical 
individuals which differed not merely in degree but in kind. These 
were as different as distinct varieties, and, when the seeds were 
planted in the garden they bred true to their kind. The only ques- 
tion now was whether they had actually arisen from typical parents. 
To test this possibility, seeds of several typical plants were planted 
in the garden; the result being not only a repetition of the peculiar 
types observed in the field, but of about a dozen other true breed- 
ing types with well-marked differences from the parent-species and 
among themselves. 
These new types De Vries considered as new elementary species 
and he called them “mutants.” They came into existence suddenly 
in one generation and, as a rule, bred true. Whatever factors were 
responsible for mutations, the seat of origin must have been in the 
germ cell and not in the soma. Consequently they were inherited 
fully from the start. The same mutations occurred in considerable 
numbers and in successive years. In one case a given mutation 
occurred only once in eight years of observation. Some mutants 
were robust and successful, others were weak and incapable of living 
under natural conditions, others were sterile. On the basis of these 
results, which are reported in detail in chapter xxiv, De Vries came 
to the conclusion that evolution was based upon the sudden appear- 
ance of new varieties or elementary species and not. upon the natural 
selection of fluctuating variations. 
The mutation theory compared and contrasted with the natural 
selection theory.—It will be recalled that the raw material upon which 
natural selection works is the minute individual or continuous varia- 
tion that is universal in all living forms and is known to be largely 
somatic in character and due to differences in environment. Darwin 
