OUR DEBT TO INSECTS. 335 



chanced to vary most in these directions would best succeed from 

 generation to generation ; and their descendants would finally become 

 so modified as to be fitted for fertilization by insects only. 



It would be needless here to allude once more to the changes in 

 shape and arrangement thus brought about by the action of the in- 

 sects. The attraction of perfume and honey, the devices of adaptation 

 and modification, by which plants allure or detain their insect visitors, 

 must be taken for granted, and we must pass on to our proper subject 

 of color. 



If, when insects were first beginning to visit flowers, there was any 

 special difference by which the pollen-bearing parts could be easily 

 distinguished from the other organs of the plant, we may be sure that 

 it would be seized upon by the insects as a guide to the existence of 

 food, and would so be further strengthened and developed in all future 

 plants of the same species. Now, we have reason to believe that just 

 such a primitive difference does exist between flowers, and leaves or 

 stems ; and that difference is one of color. Even if we look at the 

 catkins and grass-blossoms of our own day, we see that they differ 

 slightly in hue from the foliage of their respective plants. But it 

 seems not improbable that color may have appeared much more fre- 

 quently and abundantly in primitive wind-fertilized flowers than in 

 those of our own epoch ; because wind-fertilized flowers are only in- 

 jured by the visits of insects, which would be attracted by bright 

 color ; and hence natural selection would tend to keep down the de- 

 velopment of brilliant tints in them, as soon as these had become the 

 recognized guides of the insect eye. In other words, as flowers have 

 now split up, functionally speaking, into two great groups, the wind- 

 fertilized and the insect-fertilized, any primitive tendency toward the 

 production of bright leaves around the floral organs will have been 

 steadily repressed in the one group and steadily encouraged in the 

 other. 



Did such a primitive tendency ever exist ? In all probability, yes. 

 The green parts of plants contain the special coloring-matter known 

 as chlorophyl, which is essential to their action in deoxidizing the 

 carbonic acid of the atmosphere. . But, wherever fresh energies are 

 being put forth, the reverse process of oxidation is going on ; and in 

 this reverse process the most brilliant and beautiful colors make their 

 appearance. We are all familiar with these colors in autumn leaves ; 

 and we may also observe them very conspicuously in all young shoots 

 or growing branches, especially in the opening buds of spring, the 

 blanched heads of rhubarb or seakale, and the long sprays of a sprout- 

 ing potato, grown in a dark cellar. Now, the neighborhood of the 

 floral organs is just such a place where energies are being used up and 

 where color is therefore likely to appear. Mr. Sorby has shown that 

 the pigment in petals is often exactly the same as that in the very 

 young red and yellow leaves of early spring, and the crimson foliage 



