682 



SCIENTIFIC RECREATIONS. 



Fig. 785. Female flower of nettle. 



Fertilization is accomplished in two ways ; (i) by the action of the 

 wind, by which the pollen is carried away to other 

 plants ; and (2) by means of insects the bee par- 

 ticularly. These flowers are distinctive qualities 

 relatively. In the case of the pine the pollen is 

 powdery ; so those plants which are thus fertilized 

 are the diaecious species, which include the poplar, 

 the oak, and the birch, as well as the pines. These 



Fig. 7 8 4 .-Male flower of nettle. are ^j wind _ carri ed pollen plants. The nettle IS 



illustrated here with male and female 

 flowers. 



Plants fertilized by insects are visited 

 by them, and they carry away upon their 

 heads, or bodies, the pollen, which is then 

 thrust into the stigma by the insect ; or 

 perhaps birds may carry the pollen in the 

 same way after sipping the nectar, and 

 thus playing an unconscious, but most im- 

 portant, part in the economy of nature. 



We always find the ovtde at the ter- 

 mination of an axis ; it is unable to form a seed alone. The pollen grains must 



fertilize it, and in consequence many ovules come to 

 nought. The ovule is produced in the pistil, which, as 

 before stated consists essentially of two parts the 

 ovary and the stigma ; the latter secretes a fluid to 

 hold the pollen. We annex the representation of a 

 highly-magnified pistil (vertical section, fig. 786*2). 

 The pollen grains are indicated by d, attached to 

 stigma, c, projecting through the style, b, into the 

 ovary, a, and passing through the ovules. 



With the transmission of the pollen to the 

 ovary of the pistil, the functions of the anther and 

 stigma terminate ; accordingly these parts of the 

 flower rapidly wither and decay after fertilization. 

 The filaments, the style, and the petals speedily 

 participate in the decay, but the sepals remain some- 

 times persistent in an altered form. The ovary and 

 its contents alone proceed in their further develop- 

 ment, and undergo material changes, in which, 

 however, the bracts and the calyx often par- 

 ticipate. 



The fully developed and matured ovule, the 

 seed, is, of course, regarded as the essential part of 

 the fruit ; the enlarged ovary forms the pericarp, 

 Fig. 7 86.-Erect ovule. enclosing the seed. The form of the pericarp 



