II.] FORMS OF POLLEN. 43 



small, very numerous, and attached lower down, 

 separate themselves altogether from the plant, rise 

 to the surface, and fertilise the female flowers, among 

 which they float. When this is effected, the spiral 

 stalk of the female flower again contracts, and draws 

 it down below the surface. 



While the pollen grains from each flower agree very 

 closely with one another, those of different species 

 differ greatly in form, size, character of surface, &c. 

 Doubtless there are reasons for these differences, but 

 the subject is one with reference to which we have 

 as yet very little information. 



According to Sprengel, the pollen of wind-fertilised 

 flowers is drier, and therefore more easily carried by 

 the wind, than that of most insect-fertilised flowers. 

 I say of most, because in some cases, for instance 

 in the violet, as will be shown presently, it is as 

 necessary that the pollen should separate readily 

 from the anthers, as in wind-fertilised flowers. 



Mr. Bennett states that the pollen of wind-fertilised 

 flowers is generally spherical ; while that of insect- 

 fertilised flowers is usually furrowed, the furrows 

 running along the longer axis of the grain. 



In Dimorphous species the pollen of the short- 

 styled form is generally larger than that of the long- 

 styled form, but in Linum, according to Hildebrand, 

 (" Die Ges. Verth. bei den Pflanzen," p. 37) it is of the 

 same size in both forms. 



In Faramea, another Dimorphous group, the sur- 

 face of the pollen grains is different in the two forms 

 (Thome " Das Gesetz der vermiedenen Selbstbe- 

 fruchtung bei den hoheren Pflanzen," 1870), the 



