44 FORM AND QUANTITY OF POLLEN. [CHAP. 



smaller grains of the long-styled form are studded 

 with small points ; in consequence of which the pol- 

 len-grains are less easily detached from the anther ; 

 this difference possibly has reference to the different 

 position of the two forms ; the smooth ones being 

 sheltered by the flower ; while the larger pollen- 

 grains, which are produced in the anthers of the 

 long stamens, and are therefore more exposed to the 

 wind, are, in consequence of their roughness, less 

 liable to be blown away and wasted. 



According to D. Miiller ("Bot. Zeit," 1857) the pollen 

 of the small flowers of Viola elatoir and V. lancifolia 

 is minute and round. Herr von Mohl, however, found 

 no difference between the pollen of the large and 

 small flowers in V. 0>0#&("Bot Zeit," 1863). The 

 number of grains in these flowers is very small. So 

 also in the cleistogamous flowers of Oxalis acetosella, 

 there are not above two dozen pollen-grains in each 

 of the five larger anthers, and one dozen in each of 

 the five smaller ones. The ovules are about twenty 

 in number. 



It is interesting to notice that the contrivances by 

 which cross-fertilisation is favoured, or ensured, are 

 probably of a very different geological antiquity. Thus 

 as Miiller has pointed out, the special peculiarities of 

 the Umbelliferae and Compositae have been inherited 

 respectively from the ancestral forms of those orders ; 

 those of Delphinium, Aquilegia, Linaria, and Pedicu- 

 laris, from the ancestral forms of the respective 

 genera ; those of Polygonum Fagopyrum, P. Bistorta, 

 Lonicera Caprifolium, &c., from the ancestors of those 

 species ; while in Lysimachia vulgaris, Rhinanthus 



