INTERRELATIONS OF PLANTS AND ANIMALS 41 



and thus new plants. Many species of flowers are self-pollinated 

 and do not do so well in seed production if cross-pollinated, but 

 Charles Darwin found that some flowers which were self-pollinated 

 did not produce so many seeds, and that the plants which grew from 

 their seeds were smaller and weaker than plants from seeds pro- 

 duced by cross-pollinated flowers of the same kind. He also found 

 that plants grown from cross-pollinated seeds tended to vary more 

 than those grown from self-pollinated seed. This has an important 

 bearing, as we shall see later, in the production of new varieties 

 of plants. Microscopic examination of the stigma at the time of 

 pollination also shows that the pollen from another flower usually 

 germinates before the pollen which has fallen from the anthers of 

 the same flower. This latter fact alone in most cases renders it 

 unlikely for a flower to produce seeds by its o^vn pollen. Darwin 

 worked for years on the pollination of many insect-visited flowers, 

 and discovered in almost every case that showy, sweet-scented, 

 or otherwise attractive flowers were adapted or fitted to be cross- 

 pollinated by insects. He also found that, in the case of flowers 

 that were inconspicuous in appearance, often a compensation 

 appeared in the odor which rendered them attractive to certain 

 insects. The so-called carrion flowers, pollinated by flies, are 

 examples, the odor in this case being like decayed flesh. Other 

 flowers open at night, are white, and provided with a powerful 

 scent. Thus they attract night-flying moths and other insects. 



Other Examples of Mutual Aid between Flowers and Insects. — 

 Many other examples of adaptations to secure cross-pollination 

 by means of the visits of insects might be given. The mountain 

 laurel, which makes our hillsides so beautiful in late spring, shows 

 a remarkable adaptation in having the anthers of the stamens 

 caught in little pockets of the corolla. The weight of the visiting 

 insect on the corolla releases the anther from the pocket in which 

 it rests so that it springs up, dusting the body of the visitor with 

 pollen. 



In some flowers, as shown by the primroses or primula of our 

 hothouses, the stamens and pistils are of different lengths in different 

 flowers. Short styles and long or high-placed filaments are found 

 in one flower, and long styles with short or low-placed filaments 



