70 ADAPTATION AND PROGRESS 
another. One might represent the germ-plasm by the metaphor of a long 
creeping root-stock from which plants arise at intervals, these latter repre- 
senting the individuals of successive generations. 
Heredity being thus explained, variation is held to be due to the 
union of diverse sex cells? and possibly to katabolic influences 
from the environment that somehow affect the germ-plasm.° 
Huco De Vries (1848- ) 
Mutations 
Three quotations at the very beginning of De Vries’ Species 
and Varieties are suggestive of the relation between his work 
and that of Lamarck and Darwin. ‘ The origin of species is a 
natural phenomenon,” Lamarck; “ The origin of species is an 
object of inquiry,” Darwin; “The origin of species is an object of 
experimental investigation,”’ — this is the thesis of De Vries, and 
to his observations and experiments, according to Sir Arthur 
Thomson, the world is indebted for the establishment upon a 
solid basis of the theory of evolution by mutation. 
A further relation between this theory and that of Darwin is 
brought out in the closing words of the book referred to: ‘‘ Mu- 
tation explains the arrival of the fittest but natural selection the 
survival of the fittest.” That is, De Vries does not deny the 
potency of natural selection, as some have asserted, but contends 
that it is insufficient as a theory of biological evolution for it 
takes no account of the origin of change. His chief contention 
with the Darwinians is that natural selection operates to preserve 
adaptive mutations rather than mere fluctuations.* The theory 
in question is thus explained by Thomson: 
The general idea is that novel characters may suddenly appear, as it were, 
full-fledged, with considerable perfectness from the moment of their emer- 
gence, and without intergrades linking them to the parents. Furthermore. 
1 Essays upon Heredity, p. 266; cf. pp. 184f. For further explanation and illus- 
tration, see Walter, Genetics, pp. 10-13. 2 Essays upon Heredity, pp. 269 f. 
3 Weismann laid all stress on the former but in his later writings admitted the 
latter, and recent experiments have demonstrated the certainty of such source of 
variation though the range seems very limited. See infra, pp. 73 f. 
4 Species and Varieties, their Origin and Mutation, Introduction. Cf. Kellogg, 
op. cit., pp. 337 ff. 
