IV PLANT LIFE 33 



twenty- four miles : and, year after year, although the trees 

 were so far separated, the one was able to fertilize the 

 other. 



Fertilisation by Insects.— There are innumerable 

 plants the flowers of which are unable to fertilize themselves, 

 and are incapable of being fertilized by the agency of winds. 

 In some instances, too, although perfect stamens and pistils 

 occur in the same flowers, they do not develop at the same 

 time, and thus the pistils of one flower must be fertilised 

 by the pollen of another. This provision, which is called 

 cross fertilisation^ is very common, and it is a wise pro- 

 vision of nature to enable the plants to produce better seed. 

 In other instances, as in many orchids, aristolochias, &c., 

 the stamens are so situated as to be quite unable to cast 

 their pollen on to their own stigmas, or on to the stigmas 

 of other flowers ; and, therefore, the pistils could not be 

 fertilised, and the plants could not produce fruit and 

 propagate their species without the agency of insects or 

 birds. 



Most persons in the West Indies have noticed, at some 

 time or other, butterflies, bees and humming birds flitting 

 from flower to flower in the bright sunlight. The butter- 

 flies dart their long probosces right into the corollas ; the 

 bees creep into the flowers ; and the humming birds, ap- Humming 

 parently motionless, but really beating their wings with Jjo'^ers"'^ 

 wonderful rapidity, remain poised in front of a flower whilst 

 they probe it to the bottom with their long and slender 

 beaks. The humming birds, the bees, the butterflies, the The nectar 

 beetles and the moths all go to the flowers to rob the nectar andTnsects*^ 

 — a juice containing sugar secreted at the time oi pollination 

 —that is, when the stigma is ready to receive the pollen. 

 This nectar is industriously collected by bees, and it is stored 

 up by them in the form of honey. The nectar is secreted 

 by glands on the axis or stalk to which the various parts 

 of the flower are attached, and in some cases it is secreted 



D 



