334 THE POPULAR SCIENCE MONTHLY. 



shown that plants produced from the pollen of one flower applied to 

 the pistil of another are stronger and more vigorous than plants pro- 

 duced from the stamens and ovules of a single blossom. It was to 

 obtain the benefit of this cross-fertilization in a simple form that flow- 

 ers first began to exist ; their subsequent development depends upon 

 the further extension of the same principle. 



The pines and other conifers, the grasses and sedges, and the for- 

 est-trees, for the most part depend upon the wind to waft the pollen of 

 one blossom to the pistil of the next. Hence their flowers generally 

 protrude in great hanging masses, so that the breeze may easily carry 

 off the pollen, and that the pistils may stand a fair chance of catching 

 any passing grain. Flowers of some such types as these were doubt- 

 less the earliest of all to be evolved, and their colors are always either 

 green or plain brown. 



But wind-fertilization is very wasteful. Pollen is an expensive 

 product to the plant, requiring much useful material for its manu- 

 facture ; and yet it has to be turned loose in immense quantities on 

 the chance that a stray grain here and there may light upon a pistil 

 ready for its reception. It is almost as though the American farmers 

 were to throw their corn into the Atlantic in hopes that a bushel or 

 two might happen to be washed ashore in England by the waves and 

 the Gulf Stream. Under such circumstances, a ship becomes of im- 

 mense importance ; and Nature has provided just such ships, ready- 

 made for the very work that was crying out to them. These ships 

 were the yet undifferentiated insects, whose descendants were to grow 

 into bees, rose-beetles, and butterflies. 



Already, in the carboniferous world, winged insects had begun to 

 exist. Some of these must soon have taken to feeding among the 

 hanging blossoms of the first flowering plants. Insects are fond of 

 the soft and nutritious pollen ; and it would seem at first sight as 

 though they could therefore be only enemies to the plants which they 

 visited. But, as they went from flower to flower in search of food, 

 they would carry pollen from one to the other, clinging to their heads, 

 feet, or legs ; and so would unconsciously aid in fertilizing the blos- 

 soms. Though some of the pollen would thus be eaten up, yet the 

 saving effected by the substitution of the insect as a ship, for the old 

 wasteful mode of dispersal by the wind, would more than compensate 

 for the loss thus brought about. Accordingly, it would naturally hap- 

 pen that those flowers which most specialized themselves for fertiliza- 

 tion by means of insects, would gain a considerable advantage over 

 their neighbors in the struggle for existence. For this purpose, 

 their outer leaves ought to assume a cup-like shape, instead of the 

 open clusters of the wind-fertilized type ; and their form should be 

 directed rather to saving the pollen than to exposing it ; while their 

 effoi-ts must chiefly be expended in attracting the insects whose visits 

 would benefit them, and repelling all others. Those flowers which 



