POLLINATION. 



39 



the other parts, but it may be laminar, case the term Self-PoUiuation or Close- 

 It is therefore sometimes easy to mistake Pollination is applied, or they may pro- 

 a disk for a corolla, aborted stamen circle ceed from different flowers, in which case 



or crown. In all its peculiarities above 

 described, and in the number, size and 

 form of its divisions and appendages, the 

 disk is characteristic and of the greatest 

 value in classification, either generic, as 

 in the Gesneriaceae, or specific, as in 

 Eschscholtzia* 



POLLINATION. 



We have seen that the essential female 

 element of reproduction in the flower is 

 produced la the nucellus of the ovary, the 

 male within the pollen-tube. We have 

 also seen that these two elements are 



produced separately, and in most cases 

 remotely, from one another, and that some 

 means must exist for bringing them to- 

 gether in order that fertilization may be 

 effected. In those plants (Gymnosperms, 

 Figs. 192 and 193) in which no stigma 

 exists, this is accomplished by bringing 

 the pollen into immediate contact with 

 the ovule, which is exposed to external 

 contact. In those in which a stigma ex- 

 ists it is accomplished by the deposit and 

 fixation of the pollen thereupon. To 

 either of these processes the term Pollina- 

 tion is applied. The two elements may 

 proceed from the same flower, in which 



the term Cross-Pollination is applied. It 

 will be noted further that there are de- 

 grees of cross-pollination, according to 

 whether the elements proceed from flow- 

 ers upon the same or upon different 

 plants-. When the flowers are perfect it 

 is at least possible in most cases for them 

 to be either close or cross pollinated. In 

 nearly all cases the reproductive function 

 is strengthened through cross-pollination, 

 which explains the fact that nearly all 

 flowers are constructed so as to facilitate 

 cross-pollination, while most of them 

 are so constructed as to incommode, and 

 very many to prevent, close-pollination. 

 In a few cases the flower is constructed 

 so as to prevent cross-pollination. The 

 methods of effecting pollination may be 

 divided into the ordinary and the excep- 

 tional. The latter must be considered 

 individually. The former are two — 

 namely, through the agency of the wind 

 and through that of insects (or occasion- 

 ally other animals). Flowers adapted to 

 the former method are called Anemophi- 

 lous; those adapted to the latter are called 

 Kntomophilous. Occasionally the flower 

 is so formed that the movement of the 

 water during rains, or in streams, effects 

 pollination. The activity of the wind 

 being beyond the control of the flower, the 

 adaptation of the structure of an anemo- 

 philous flower is limited to securing the 

 benefits of such action when it comes into 

 play. This consists chiefly in (1) a Gre- 

 garious Habit — the growing together in 

 great numbers of individuals of one kind, 

 as an the case of grasses and of most of 

 the forest trees of temperate latitudes; 

 (2) a very abundant pollen (3), which is 

 loosely fixed (Fig. 229, one method), light 

 and easily removed and transported, and 

 (4) the disposition of the ovule of gym- 

 nosperms, and the form and disposition of 

 the stigma and connected parts of an- 

 giosperms, so as to catch the pollen. All 

 these provisions may be readily seen to 

 affect the process in the case of Pinus 

 palustris, for example. 



In entomophilous flowers such pro- 

 visions must be preceded by others of a 

 different nature, calculated to attract and 



