THE AMERICAN NATURALIST [Vol. XLIII 



become, in the long course of development, securely in- 

 closed beneath a thick coat of husks, impenetrable by 

 nearly all insects ; and we may perhaps reasonably infer 

 that, among the possible injuries against which this con- 

 spicuous protective structure defends the soft young 

 kernel, those of insects are to be taken into account. 



There are, of course, many insect species, even among 

 those which habitually frequent the plant, which are un- 

 able to appropriate certain parts of its substance to 

 their use, but this is because of the absence of adaptation 

 on their part and not because of any special defensive 

 adaptation on the side of the plant. Thus we may say 

 that, with the exception of the ear, the whole plant lies 

 open and free to insect depredation, and that it is able 

 to maintain itself in the midst of its entomological de- 

 pendents only by virtue of its unusual power of vigorous, 

 rapid and superabundant growth. Like every other 

 plant which is normally subject to a regular drain upon 

 its substance from insect injury, it must grow a surplus 

 necessary for no other purpose than to appease its 

 enemies ; and this, in a favorable season, the corn plant 

 does with an energetic profusion unexampled among our 

 cultivated plants. Insects, indeed, grow rapidly as a 

 rule, and most of them soon reach their full size. Many 

 species multiply with great rapidity, but even these the 

 corn plant will outgrow, if given a fair chance, provided 

 they are limited to corn itself for food. 



Turning to the other side of the relationship, we may 

 say that the corn insects exhibit no structural adaptations 

 to their life on the corn plant— no structures, that is to 

 say, which fit them any better to live and feed on corn 

 than on any one of many other kinds of vegetation. 

 This was, of course, to be expected of the great list of 

 insects which find in corn only one element of a various 

 food, and that not necessarily the most important ; but it 

 seems equally true of those which, like the corn root- 

 worm or the corn root-aphis, live on it by strong prefer- 

 ence, if not by absolute necessity. 



