borne away by the insect, and that it be deposited upon the stigma, 

 are very numerous and very wonderful. Some of them are so intri- 

 cate as to seem almost incredible unless we remember how jealously 

 nature guards the type. 



It sometimes happens that particular plants can only be pollinated 

 by particular insects, a fact which largely explains many irregularities 

 in flower forms. For example, the common red clover can only be 

 pollinated through the agency of the bumble-bee. If the bumble- 

 bees in any given region were completely exterminated, the red clover 

 would fail to set seed and would, in a very short time, become extinct. 

 In many cases where the red clover blooms very early farmers do not 

 expect the first flowers to set seed, because, as they say, "the flowers 

 blossomed before bee-time." Because of the purposeful movements 

 of the insect from flower to flower in search of food, pollination is 

 much more certainly assured than in the case of wind-pollinated 

 flowers, and there is a corresponding reduction in the amount of the 

 pollen. 



We here begin to see how tangled is the web of life, how closely 

 interdependent are life forms. The plant furnishing food for the 

 insect, the insect in its turn insuring the perpetuation of the plant 

 form. The more we study nature, the closer and more wide-reaching 

 will these relations be found, until we see that the fullest study of a 

 single form would in the end include all living organisms. 



But, whether the pollinating agent is wind or insect, it would be 

 possible in many cases that self-pollination would occur did not spe- 

 cial devices for its prevention intervene. The more apparent of these 

 are the following: 



1. Stamens in one flower and pistils in another, though upon the 

 same plant. 



2. Stamens in the flowers of one plant, pistils in those of another. 



3. Pollen maturing before the stigma is in condition to receive it, 

 or the reverse. 



It is very evident that any one of these conditions will effectually 

 prevent self-pollination. The existence of these conditions is easily 

 made out by an examination of the flowers, although the last may 

 need a word of explanation. The maturing of the pollen is evidenced 

 by the bursting of the anther for its escape, and the subsequent droop- 

 ing of the filaments. The indication of the stigma being in a condi- 

 tion to receive the pollen is ordinarily the development, upon a more 

 or less definitely marked region, of hairs or a mucilaginous substance 

 \\"hich will serve to retain the pollen which falls upon it. 



