vi] FIXITY OF POSITION IN PLANTS 93 



mutually adaptable, and indeed mutually dependent, 

 certain plants and insects are upon one another. No 

 better example of this can be quoted than that of the 

 genus Aconitum (Monkshood), and the humble-bees 

 that pollinate it. The northern limits of distribution 

 of the two in Asia coincide with an exactitude that 

 can only mean an intimate biological relation. This 

 is not the place to describe such observations in detail, 

 but rather to consider the conditions which have made 

 it necessary to resort to such artifices, and the evolu- 

 tionary steps which may have led to their adoption. 

 These conditions, simple though they may be, are 

 frequently overlooked by those who pursue this 

 branch of observation, or omitted from popular state- 

 ments on the subject. Their recognition, however, 

 must underly any rational study of pollination. 



The Flowering plants of the land were without 

 doubt evolved from Fern-like plants, and these again 

 are generally held to have originated from the 

 primitive Algal Flora of the water. In such organ- 

 isms as these the male cells, and sometimes the 

 female also, are capable of independent movement 

 in water, into which they are extruded at maturity 

 (compare Fig. 2). And if they come, as they frequently 

 of necessity do, from different parent plants, the cross- 

 ing is easily effected as a consequence of their own 

 independent powers of movement. In the Pterido- 

 phytes such as the Ferns, we see organisms which, 



