62 NATURAL HISTORY 



sperm cells, which are thus enabled to unite, each with a single egg 

 cell, in the ovule of the pistil. The union of the sperm nucleus with 

 its egg nucleus is called fertilization. As a result of this process the 

 fertilized egg develops into an embryo or young plant which is held 

 in the seed. When favorable conditions arise, this embryo m.ay 

 develop into a plant. 



Bees are the chief pollinizing agents, although butterflies, moths, 

 flies, and a few other insects perform this service as well. Hum- 

 mingbirds often pollinate tubular flowers, while other small birds, 

 snails, and even bats are agents in the pollination of certain forms. 

 Man and animals may accidentally pollinate flowers in brushing past 

 them through the fields. The value of cross-pollination is obvious 

 and is an example of the close weaving of life in which man, animals, 

 and plants are all inescapably entangled. 



SUGGESTED READINGS 



Borradaile, L. A., The Animal and Its Environment, Oxford University Press, 



London, 1923. Chs. IV, V, XIV. 



Excellent for reference. 

 Elton, C, Animal Ecology, The Macmillan Co., 1935. Chs. V, VI, VIII. 



Particularly valuable on the animal community and the relationship of 



animals to a food supply. 

 Needham, J. C, and Lloyd, J. T., Life of Inland Waters, 2nd ed., Charles C. 



Thomas, 1930. Ch. V. 



Interrelationships among fresh-water organisms. 

 Pearse, A. S., Animal Ecologij, McGraw-Hill Book Co., 1926. Chs. VIII, X. 



A wealth of material on interrelationships. 

 Rau, Phil., Jungle Bees and Was-ps of Barro Colorado Island, privately printed, 



Kirkwood, St. Louis, 1933. 



An ecological study of a tropical environment. 

 Wallace, A. R., The Geographical Distribution of Animals, 1876. Books I 



and II. Ch. IV, especially. 



This book forms the basis for most of the modern work in distribution. 



All of Part III, Books I and II, is extremely interesting. 

 Weaver, J. E., and Clements, F. E., Plant Ecology, McGraw-Hill Book Co., 



1935. Ch. XVI. 



An interesting chapter on relations between plants and animals, with 



especial emphasis on insect pollination. 

 Wells, H. G., Huxley, J. S., and Wells, C. P., The Science of Life, Doubleday, 



Doran & Co., 1931. Book 6, Chs. IV and V. 



A fascinating book for general reading. 



