BQTANICAL EVOLUTION. 363 
this particular kind, we may find one varying in some detail—such as 
period of ripening, form of grain, or other slight character—and we 
may succeed in transmitting this variation through many generations, 
and intensifying it. Now in doing this artificially on a small scale, 
we are only putting into operation in a special direction, a law that 
nature applies directly on a very large scale. Only it is very difficult 
to see the operation of the law in a state of nature. For while we 
often perpetuate what would be most unfavourable variations in a 
state of nature—as for example, among all our domestic animals and 
florists’ flowers—these, if left strictly to the action of natural laws, 
would be promptly suppressed. 
I have already said that we do not know—except in a very slight 
degree—the causes of variations among living organisms, but no 
doubt many of them arise directly from the conditions under which 
the organisms live. A change in the environment in any way— 
however slight—may profoundly affect all the living organisms 
subjected to its influence, and as a stone dropped into the Pacific 
Ocean here would transmit an influence to the shores of America, 
so this influence of the environment—whether it be climatic or 
otherwise—aftects all nature directly or indirectly. This may be 
stated another way, namely, that all the relations among living 
organisms and their surroundings are so complex, that a change in 
one form affects all the others more or less. Let me quote an 
example of this from the “ Origin of Species.” 
Darwin says (p. 57)—“I find from experiments that humble- 
bees are almost indispensable to the fertilisation of the heartsease 
(Viola tricolor), for other bees do not visit this flower. I have also 
found that the visits of bees are necessary for the fertilisation of some 
kinds of clover: for instance, 20 heads of Dutch clover (7rifoliwm 
repens) yielded 2,290 seeds, but 20 other heads protected from bees 
produced not asingle seed. Humble-bees alone visit red clover, as 
other bees cannot reach the nectar. . . . . Hence it is highly 
probable that, if the whole genus of humble-bees became extinct or 
very rare in England, the heartsease and red clover would become 
very rare or wholly disappear. The number of humble-bees in any 
district depends on the number of field-mice, which destroy their 
combs and nests; aud Col. Newman, who has long attended to the 
habits of humble-bees, believes that ‘more than two-thirds of them 
are thus destroyed all over England.’ Now the number of mice is 
largely dependent, as everyone knows, on the number of cats; and 
Col. Newman says, ‘ Near villages and small towns I have found the 
nests of humble-bees more numerous than elsewhere, which I 
attribute to the number of cats that destroy the mice.’ Hence it is 
quite credible that the presence of a feline animal in large numbers 
in a district might determine, through the intervention first of mice 
and then of bees, the frequency of certain flowers in that district!” 
It is manifest that cases like this cited by Darwin might be 
extended indefinitely, and we in New Zealand have some little 
practical experience already of the influence exerted by and on 
animals and plants by the numerous introduced species of both which 
are changing the face of this country. 
Of the variations which continually arise among living organisms,. 
some may be beneficial, and some positively injurious, but how far a 
variation is one or the other, we are only imperfectly capable of 
