416 SEXUAL RELATIONS OF PLANTS. CHAP. X 



Finally, we have seeii 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 dioacious. 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 duals, which represented the two 



amount of evidence that all the incipient sexes. On this view, the 



higher animals are the descend- higher animals may now owe 



ants of hermaphrodites ; and it is their bilateral structure, with all 



a curious problem -whether such their organs double at an early 



hermiphroditism may not have embryonic period, to the fusion 



been the result of the conjugation or conjugation of two primordial 



of two slightly different indivi- individuals. 



