CHAP, i.] PLANT ARCHITECTURE. 23 



when the presence of water enables the motile anthero- 

 zoids or fertilizing bodies to find their way to the female 

 element. It is impossible to enter into details in con- 

 nection with this subject of fertilization, but it may 

 be stated that the portion of the plant producing the 

 sexual organs is usually very small, and could be covered 

 by a dewdrop, which would afford a superabundance of 

 water for the purpose of enabling the antherozoid to 

 swim about and come in contact with the passive female 

 element. All plants having the male element of the 

 sexual generation possessed of spontaneous movement 

 belong to the class of plants called Cryptogams, which 

 constitutes one of the two primary subdivisions of the 

 Vegetable Kingdom. As plants receded more and more 

 from their primitive aquatic habitat, and became differen- 

 tiated so as to carry on their entire existence on dry land, 

 the sexual mode of fertilization by motile antherozoids 

 that reached the female by swimming, became untenable, 

 and by degrees a radical change took place in the struc- 

 ture of the male or fertilizing body. Instead of the 

 naked, spontaneously moving antherozoid, the fertilizing 

 bodies took the form of minute cells inclosed in a cell- 

 wall and entirely devoid of spontaneous movement ; 

 these cells or pollen-grains were produced in considerable 

 numbers in the immediate neighbourhood of the female 

 organs, on to which they were shed when mature, thus 

 the agency of water as the medium by which the male 

 element reached the female was dispensed with. By the 

 above arrangement it will be observed that both male 

 and female elements were produced by the same plants, 

 consequently self-fertilization resulted. Owing to the 

 great advantages of cross-fertilization (when the male and 



