92 PLANT-LIFE ON LAND [OH. 



bulatory organisms, such as the higher animals, the 

 search for a mate is readily carried out. But where 

 the organism is fixed, that fact at once places fertili- 

 sation and still more intercrossing at a disadvantage. 

 It is obvious that in them special means will have to 

 be provided in order to ensure its taking place. 

 When the importance of intercrossing is fully realised, 

 as well as the embargo on its ready occurrence which 

 follows from the fixity of position, it becomes in- 

 telligible that the sacrifices to secure it should be 

 great, and the means employed various and even 

 recondite. 



Few subjects within the scope of botanical science 

 have raised more interest for the general reading 

 public than the cross-pollination of Flowering plants. 

 Ever since the time of Sprengel, who first demonstrated 

 the importance of animal agency for this end, and 

 drew attention to the specialisation of flowers as 

 mechanisms which should co-operate with the active 

 insect, the interest has been on the increase. But it 

 was specially stimulated in later years by the writings 

 of Darwin, and of Muller, and has been expanded by 

 the observations of many other authors. It is now 

 a matter of common knowledge that not only are 

 insects, snails, birds and even bats made use of as 

 the carriers of pollen from flower to flower, but the 

 natural motor impulses of winds and moving water 

 are also employed. It has also been pointed out how 



