160 PLANT-LIFE ON LAND [OH. 



for securing cross-pollination. The wind, occasionally 

 water, but chiefly animal agencies have been brought 

 into the service of intercrossing. The full armoury 

 of colour, of honey, and of scents, together with 

 elaborate mechanical devices, contribute to this end. 

 Their study has become almost a play-ground of 

 science. The flower has developed into a highly 

 specialised mechanism for the purpose of intercrossing. 

 First came the segregation of the nutritive and pro- 

 pagative regions of the originally non-specialised 

 shoot, by such steps as are illustrated among the 

 lower Vascular plants. The propagative region then 

 gradually assumed the features of the flower as it 

 is seen in such various forms at the present day 

 (Chapter IV). But while we recognise to the full 

 the beauty and the almost infinite variety of the 

 methods employed to secure cross-pollination, the 

 fact that stands behind them all, and is indeed their 

 ultimate justification, is the immobility of the plant, 

 so different from the ambulatory powers of the 

 higher animals. The plant cannot move as a whole 

 to seek its mate, and so if intercrossing is to take 

 place at all, external agencies must be pressed into 

 the service. 



The same fact is the ultimate raison d'etre of 

 the varied methods of dispersal of seeds and fruits 

 (Chapter VII). It has been seen how great is the 

 fecundity of many land growing plants. But the 



