WASPS, ANTS AND BEES 199 



has long been recognized, and some orchard growers keep 

 hives of bees in or near their orchards to ensure the advantage 

 of cross-pollination to their trees. 



Cross-pollination is simply the bringing of pollen from one 

 plant individual to the flowers of another individual of the same 

 species. Self-pollination is the getting of pollen from the 

 stamens of one flower on to the stigma of the same flower. 

 The advantage of cross-pollination, as first experimentally 

 proved by Darwin, and since then confirmed by other experi- 

 menters and, without scientific intention but none the less 

 effectively, by hosts of economic plant-breeders (horticul- 

 turists, florists, etc.), lies in the fact that the seeds produced 

 when the ovules of one plant are fertilized by the sperm-cells 

 (in the pollen) of another, develop plant individuals of mark- 

 edly stronger growth (shown in size of plant and its fruits, in 

 number of seeds, etc.), than seeds produced by the fertilization 

 of ovules by sperm-cells of the same plant. For the sake of 

 insuring this cross-pollination the flowers of many plants are 

 highly specialized. This specialization follows two general 

 lines: One includes means of preventing self-pollination such 

 as having stamens and pistils ripen at different times, or be of 

 such different lengths that the pollen cannot fall on the pistils 

 in the same flower, etc. The other line includes means for 

 attracting insects, such as color and pattern and the secretion 

 of nectar, and means, such as shape, curious modification of 

 flower parts, etc., to compel the visiting insects both to leave 

 on the stigma pollen brought from other flowers and to carry 

 away from the anthers pollen from the flower being visited. 

 Honey bees are undoubtedly the most important of all insects 

 concerned with cross-pollination, and perform in this way a 

 great service to flower and orchard growers. 



The Ants. The ants constitute the fifth and last principal 

 group of Hymenoptera, and for their adequate treatment a 

 book much larger than the whole of this one would be necessary. 

 Such a book, indeed, has been recently written by Professor 

 W. M. Wheeler, 1 the foremost American student of ants, and 



1 Wheeler, W. M. Ants, their Structure, Development and Behavior, 

 1910. 



