DEVICES TO SECURE CROSS-POLLINATION 



being like that of decayed flesh. Other flowers open at night and 

 are white, besides having a powerful scent. Thus they attract 

 night-flying moths and certain other insects. 



Other Devices to secure Cross-Pollination. — There are many 

 other examples of adaptations to secure cross-pollination by means 

 of the visits of insects. The mountain laurel 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 plants, self-pollination is prevented by certain devices, 

 as in the primroses, in which the stamens and pistils are of different 

 lengths in different flowers. Short 

 styles and long filaments with high- 

 placed anthers are found in some 

 flowers, and long styles and short 

 filaments with low-placed anthers in 

 others. Pollination is most likely 

 to be effected by some of the pollen 

 from a low-placed anther reaching 

 the stigma of a short-styled flower, 

 or by the pollen from a high anther 

 being placed upon a long-styled 

 pistil. There are, as in the case of 

 the spiked loosestrife, flowers hav- 

 ing pistils and stamens of three 

 lengths. Pollen grows best on pistils of the same length as the 

 stamens from which it came. The stamens and pistil ripen at 

 different times in some flowers. The " Lady Washington " gera- 

 nium, a common house plant, shows this condition. Here cross- 

 pollination must take place if seeds are to be formed.^ 



Special Adaptations between Flowers and Insects. — A very 

 remarkable instance of insect help is found in the pollination of the 

 yuc'ca, a semitropical lily which lives in deserts (to be seen in most 



The condition of stamens and pistils 

 on the spiked loosestrife. 



1 For an excellent account of cross-pollination of milkweed, the reader is re- 

 ferred to W. C. Stevens, Introduction to Botany. Orchids are well known to botan- 

 ists as showing some very wonderful adaptations. A classic easily read is Darwin, 

 On the Fertilization of Orchids. 



H. NEW CIV. BIOL. — 4 



