438 THE EVOLUTION OF LIFE. 



between the actions in the organism and the actions in its 

 environment; seeing that all other things remaining the 

 same, if these defences were absent, the destruction by herb- 

 ivorous animals would be so increased, that the number of 

 young plants annually produced would not suffice, as it now 

 does, to balance the mortality, and the species would there- 

 fore disappear. But these defensive appliances, though they 

 aid in maintaining the balance between inner and outer 

 actions, cannot have been .directly called forth by the outer 

 actions which they serve to neutralize; for these outer 

 actions do not continuously affect the functions of the plant 

 even in a general way, still less in the special way required. 

 Suppose a species of nettle bare of poison-hairs, to be habit- 

 ually eaten by some mammal intruding on its habitat ; the 

 agency of this mammal would have no direct tendency to 

 develop poison-hairs in the plant; since the individuals 

 devoured could not bequeath changes of structure, even were 

 the actions of a kind to produce them ; and since the in- 

 dividuals that perpetuated themselves, would be those on 

 which the new incident force had not fallen. An- 



other class of organs similarly circumstanced, are those of 

 reproduction. Like the organs of defence, these are not, 

 during the life of the individual plant, variably exercised by 

 variable external actions; and therefore do not fulfil those 

 conditions under which structural changes may be directly 

 caused by changes in the environment. The generative 

 apparatus contained in every flower, acts only once during 

 its existence ; and even then, the parts subserve their ends 

 in a passive rather than an active way. Functionally-pro- 

 duced modifications are therefore out of the question. If a 

 plant's anthers are so placed, that the insect which most 

 commonly frequents its flowers, is sure to come in contact 

 with the pollen, and to fertilize with it other flowers of the 

 same species; and if this insect, dwindling away or dis- 

 appearing from the locality, leaves behind no insects that 

 have such shapes and habits as cause them to do the same 



