FERTILIZATION OF FLOWERS. 297 



into leaves, as in tlic green rose. This is a reason also for the 

 fact that plants often fail to blossom in conscciucnce of too much 

 vegetative vigor, which may be overcome by root pruning, by 

 confinement of the roots in a limited space, or by a scanty 

 supply of water or food. 



Though we are often inclined to accept as literal truth the 

 words of the poet, — 



" Full many a flower is born to blush unseen, 

 And waste its fragrance on the desert air," — 



yet, the beautiful colors, the peculiar odors and the honeyed 

 sweetness with which they are endowed, by no means fail to 

 accomplish a useful purpose. By these attractions countless 

 insects are enticed to fly from plant to plant, and so to transport 

 the fertilizing pollen which would otherwise rarely attain its 

 proper destination. Without entering at all into doubtful ques- 

 tions of vegetable physiology, we may state that the production 

 of seeds and spores capable of germination presupposes the 

 impregnation of ovules or spore-cells by pollen grains or some 

 corresponding bodies. While the great majority of flowers con- 

 tain both sets of sexual organs, yet sometimes they are found 

 upon separate plants. It is believed that in most cases, pollen 

 is efficient in fertilizing the ovules of some other flower than the 

 one by which it is produced — in other words, self-impregnation, 

 if possible, is by no means common. Fertilization is, therefore, 

 usually effected either through the agency of the wind, of insects 

 or of man transporting the pollen from one flower or plant to 

 auotlier. The only species which has from time immemorial 

 been thus artificially impregnated for the production of fruit is 

 the date palm, which bears the stamens and pistils upon differ- 

 ent trees. The caprification of the fig in the Levant, performed 

 by hanging branches of the wild tree upon the cultivated at the 

 time of flowering, is designed to effect the same object by the 

 introduction of insects into the young fruit. It does not ap- 

 pear, however, to be of any special advantage, though long 

 practised. 



Artificial impregnation of ovules and spores, though unneces- 

 sary in ordinary cases to the development of fruit, has assumed 

 in recent times great interest and importance from the fact that 

 it affords the means of securing new and valuable varieties of 



38 



