CHAP. X. SEXUAL RELATIONS OF PLANTS. 411 



either monoecious with their sexes separated on the 

 same plant, or dioecious with their sexes on distinct 

 plants. In the class Monoecia of Linnaeus, Delpino 

 shows* that the species of twenty-eight genera are 

 anemophilous, and of seventeen genera entomophilous. 

 In the class Dioecia, the species of ten genera are 

 anemophilous and of nineteen entomophilous. The 

 larger proportion of entomophilous genera in this 

 latter class is probably the indirect result of insects 

 having the power of carrying pollen to another and 

 sometimes distant plant much more securely than the 

 wind. In the above two classes taken together there 

 are thirty-eight anemophilous and thirty-six ento- 

 mophilous genera ; whereas in the great mass of 

 hermaphrodite plants the proportion of anemophilous 

 to entomophilous genera is extremely small. The 

 cause of this remarkable difference may be attributed 

 to anemophilous plants having retained in a greater 

 degree than the entomophilous a primordial condi- 

 tion, in which the sexes were separated and their 

 mutual fertilisation effected by means of the wind. 

 That the earliest and lowest members of the vegetable 

 kingdom had their sexes separated, as is still the case 

 to a large extent, is the opinion of a high authority, 

 Nageli.f It is indeed difficult to avoid this con- 

 clusion, if we admit the view, which seems highly 

 probable, that the conjugation of the Algae and of 

 some of the simplest animals is the first step towards 

 sexual reproduction ; and if we further bear in mind 

 that a greater and greater degree of differentiation 

 between the cells which conjugate can be traced, 

 thus leading apparently to the development of the 



* Studi sopra un Lignaggio t ' Entetehung nnd Begriff del 

 anemofilo delle Composite,' 1871. naturhist. Art,' 1865, p. 22. 



