OUR DEBT TO INSECTS. 339 



color-sense exists only in those animals whicli would be decidedly 

 benefited by its possession. And for these reasons it seems improba- 

 ble that insects ever developed such a faculty until the need for it 

 arose among the beautiful flowers. 



Now that we have arrived at this theoretical conclusion, let us 

 hark back again for a while to the reactions which the color-sense, 

 thus aroused, produced upon the flowers which gave it birth. 



We may take, as a capital example of an insect-fertilized flower, 

 an English dog-rose. Compare this mentally with the wind-fertilized 

 blossoms, such as grasses and catkins, and it is at once obvious that 

 the great difference between them consists in the presence of a col- 

 ored corolla. No wind-fertilized plant ever has a whorl of gay petals ; 

 and though the converse is not quite true, yet almost all insect-ferti- 

 lized plants are noticeable for their brilliant tints of red, white, blue, 

 or yellow. The structures in which these pigments reside have no 

 function whatsoever, except that of attracting the insect eye. They 

 are produced by the plant at an enormous physiological expense ; and, 

 if their object were not to secure the visits of insects, they would be 

 just so much dead loss to the species. Nor is it only once that these 

 colored corollas have been developed. They occur, quite independ- 

 ently, in both great divisions of flowering plants, the monocotyledons 

 and the dicotyledons. This coincidence could hardly have happened 

 had it not been for that original tendency which we already noticed 

 for pink, scarlet, or orange pigments to appear in the neighborhood of 

 the floral organs. Nor is it twice only, in all probability, that flowers 

 have acquired bright petals through insect visits, but a thousand times 

 over. In almost every family, insect-fertilized, self-fertilized, and 

 wind-fertilized species are found side by side, the one with brilliant 

 petals, the others with small, green, and inconspicuous flowers. 



For comparison with the dog-rose, one could not find a better type 

 than that common little early spring blossom, the dog's mercury. It 

 is a wind-fertilized flower, and it does not wish to be seen of insects. 

 Now, this mercury is a very instructive example of a degenerate green 

 flower. For, apparently, it is descended from an insect-fertilized 

 ancestor with bright petals ; but, owing to some special cause, it has 

 taken once more to the old wasteful habit of tossing its pollen to the 

 wandering winds. As a consequence it has lost the bright corolla, 

 and now retains only three green and unnoticeable perianth-pieces, no 

 doubt the representatives of its original calyx. Almost equally in- 

 structive is the case of the groundsel, though in this case the process 

 of degradation has not gone quite so far. Groundsel is a degenerate 

 composite, far gone on the way of self-fertilization. No class of flow- 

 ers have been more highly modified to suit the visits of insects than 

 the composites. Hundreds of their tubular bells have been crowded 

 on to a siiigle head, so as to make the greatest possible attractive dis- 

 play ; and in many cases the outer blossoms of the head, as in the 



