416 



SEXUAL RELATIONS OF PLANTS. 



Chap. X. 



Finally, we have seen reason to believe that the 

 higher plants are descended from extremely low forms 

 which conjugated, and that the conjugating indi- 

 viduals differed somewhat from one another, the one 

 representing the male and the other the female so 

 that plants were aboriginally dioecious. At a very 

 early period such lowly organised dioecious plants 

 probably gave rise by budding to monoecious plants 

 with the two sexes borne by the same individual ; and 

 by a still closer union of the sexes to hermaphrodite 

 plants, which are now much the commonest form.* 

 As soon as plants became affixed to the ground, their 

 pollen must have been carried by some means from 

 flower to flower, at first almost certainly by the wind, 

 then by pollen-devouring, and afterwards by nectar- 

 seeking insects. During subsequent ages some few 

 entomophilous plants have been again rendered anemo- 

 philous, and some hermaphrodite plants have had their 

 sexes again separated; and we can vaguely see the 

 advantages of such recurrent changes under certain 

 conditions. 



Dioecious plants, however fertilised, have a great 

 advantage over other plants in their cross-fertilisation 

 being assured. But this advantage is gained in the 

 case of anemophilous species at the expense of the 

 production of an enormous superfluity of pollen, with 

 some risk to them and to entomophilous species of 

 their fertilisation occasionally failing. Half the in- 

 dividuals, moreover, namely, the males, produce no 



* There is a considerable 

 amount of evidence that all the 

 higher animals are the descend- 

 ants of hermaphrodites ; and it is 

 a. curious problem whether such 

 hermiphroditism may not have 

 been the result of the conjugation 

 of twc slightly different indivi- 



duals, which represented the two 

 incipient sexes. On this view, the 

 higher animals may now owe 

 their bilateral structure, with all 

 their organs double at an early 

 embryonic period, to the fusion 

 or conjugation of two primordial 

 individuals. 



