ASSIMILATIVE COLOURATION. 387 
as a law acting through space and time; so that we narcotise our 
mind with a new dogma: not that in the beginning was the 
*‘ word,” but *‘ natural selection.” 
This endeavour to make natural selection the all and all of 
evolution* has in some cases brought about a reaction which 
denies its efficacy in toto. Thus the Rev. G. Henslow, in a 
recent interesting work, ascribes the origin of species “to the 
joint action alone of two great factors of evolution—variability 
and environment.” Mr. Henslow does good service in recording 
a large number of facts and observations, which go to prove to 
demonstration that the environment largely induces the form and 
structure of vegetable life, and he formulates the proposition that 
these features are due ‘“‘to the responsive power of protoplasm, 
which, under the influences of the external forces of the environ- 
ment, builds up just those tissues which are the best fitted to be 
in harmony with the environment in question.” +t But, alas! 
La phrase est le tyran de notre siécle. The term ‘“‘ responsive 
power of protoplasm ”’ is, like that of “germ plasm,” workable, 
but unprovable. It refers to a fact, and seeks to explain it by a 
suggestion. But even if we accept this ‘“‘ responsiveness of 
protoplasm to the environmental conditions,” natural selection is 
not banished, but only limited. It is still a cause, but not an 
absolute one; it has had an elementary and preserving process 
in a stage of life it did not create. Thus, if spinescent characters 
in plant-life seem undoubtedly due to drought, and usually 
possess an arid environment, as one may read who ever gazes on 
the Transvaalian veld, plants still survive, and could only have 
survived the effects of the foraging powers of the immense herds 
of ruminants which formerly swarmed over the land, by the 
possession of spines of defence.{ Although these animals are 
* Darwin himself distinctly stated, and again reaffirmed, ‘‘I am con- 
vinced that natural selection has been the main but not the exclusive means 
of modification” (‘ Origin of Species,’ sixth edition, p. 421). 
+ ‘Origin of Plant-Structures,’ p. 14. 
{ Dr. Meyer, quoting Grisebach (‘ Vegetation der Erde’), and detailing 
_his own observations in Hast Africa, writes:—‘‘ The plants are protected on 
the one hand against drought, and on the other against animals, by a partial 
suppression of the leaves, of which in a certain number the fibro-vascular 
bundles become indurated and form thorns from an inch and a half to two 
incheslong. . . . It is self-evident that with such a suppression of the foliage 
