vi] FIXITY OF POSITION IN PLANTS 95 



The origin of Seed-plants having this requirement 

 dates back to the most ancient epoch which has left 

 to us any remains of terrestrial plants. The earliest 

 Seed-plants (Gymnosperms) were probably as de- 

 pendent for pollination upon external agencies as 

 are the Seed-plants of the present time. Moreover, 

 since in most of these the male and female flowers 

 were distinct from one another, the carrying out of 

 pollination was for them a condition of setting seed 

 at all, not merely a condition of securing the ad- 

 vantages which follow from intercrossing. The call 

 for external help was thus not merely a matter of 

 advantage, but of imperious necessity. 



There is no clear evidence how the earliest Seed- 

 plants were pollinated. The fact that the pollen was 

 transferred is proved by its observation actually 

 within the orifice of the ovule, in sections of fossils 

 of Carboniferous age. The grains were relatively 

 large and smooth, so that though the agency of 

 transfer may have been the wind, there was no 

 definite specialisation to that end. Certainly the 

 wind is the usual means of conveyance of the pollen 

 in the Gymnosperms of the present day, though 

 among them are some which rely upon insect agency ; 

 and it is quite possible that among their early corre- 

 latives the latter may have figured more largely than 

 has hitherto been believed. But whatever may have 

 been the case for the more primitive Seed-plants, it 



