238 FERTILIZATION OR FECUNDATION. 



reproduction, there is also a formation of new cells by a constant 

 process of fissiparous or merismatic division (f 24), which may be 

 considered as analogous to the formation of buds, and which per- 

 haps depends on certain changes similar to fecundation going on in 

 the interior. 



494. In flowering plants, various provisions are made for insuring 

 the application of the pollen to the stigma. The comparative length 

 of the stamens and pistils, their position, and the dehiscence of the 

 anthers, are all regulated with this view. The existence of spiral cells 

 in the endothecium has reference apparently to the bursting of the 

 anther, and the scattering of the pollen. The number of pollen-grains 

 produced is also very great. Hassall says that a single head of Dande- 

 lion produces upwards of 240,000, each stamen of a Pa3ony 21,000, a 

 Bulrush 144 grams by weight. It has been stated, that a single plant 

 of Wisteria sinensis produced 6,750,000 stamens, and these, if perfect, 

 would have contained 27,000,000,000 pollen-grains.* In the case 

 of Evergreens, such as Firs, the quantity of pollen is enormous, 

 apparently to insure its application notwithstanding the presence of 

 leaves. The pollen from pine forests has been wafted by the winds 

 to a great distance, and is said to have fallen on the ground like a 

 shower of sulphur. 



495. The quantity of pollen required for impregnation varies. 

 Koelreuter says, that from fifty to sixty grains of the pollen of Hibiscus 

 Trionum are required to fecundate the fruit completely, containing 

 about thirty ovules. The ovary of Nicotiana, Datura, Lychnis, and 

 Dianthus, according to Gartner, may be completely fertilized by the 

 pollen of a single perfect anther. In Geum, from eight to ten 

 anthers, out of eighty-four to ninety-six contained in each flower, are 

 sufficient to fertilize from eighty to one hundred and thirty ovules 

 contained in the ovary. 



496. In many trees in which the organs of reproduction are in 

 separate flowers (as Hazel and Willow), the leaves are not produced 

 until fertilization has been effected. The protection of the pollen from 

 the direct influence of moisture, is effected by the closing of the flow- 

 ers, by the elasticity of the anther-coat only coming into play in dry 

 weather; and in aquatics, either by a peculiar covering, as in Zostera, 

 or by the flowers being developed above water, as in Nymphaea, Lo- 

 belia, Stratiotes, and Hottonia. In VaUisneria spiralis, a plant growing 



* The following estimate was made of the amount of flowers, stamens, &c., in a single specimen 

 of Wisteria sinensis: 



Number of clusters of Flowers, 9,000 



individual Flowers, 675,000 



Petals, 3,375,000 



Stamens, 6,750,000 



Ovules, 4,050,000 



For the purpose of fertilizing these ovules, the anthers, if perfect, would have contained about 



27,000,000,000 pollen-grains, or about 7000 grains to each ovule. 



