INTRODUCTION xiii 



v 



Primulas, yet in other cases it is evidently the result of 

 adaptation to local conditions; whether brought about 

 solely by the operation of natural selection, or partly 

 also by the direct action of external influences, it is not 

 necessary to inquire. A large number of instances could 

 be named in which species belonging to the same genus, 

 and therefore nearly related to one another, differ from 

 one another in having more or less conspicuous flowers 

 according as they grow at a higher or a lower elevation. 

 It will be necessary only to remind the botanical reader 

 of such genera as Anemone, Ranunculus, Dianthus, Pru- 

 nella, Salvia, and Scutellaria. On the other hand, the 

 number of fragrant plants is probably smaller at high 

 than at low altitudes; the reason being no doubt that, 

 whatever may be the purpose served by the odour of 

 flowers, it would be neutralised by the strong winds 

 which so constantly prevail among the mountains. The 

 explanation usually offered of the bright colour and 

 large size of alpine flowers is that it is necessary for the 

 attraction of the comparatively small number of winged 

 insects which inhabit the regions of the Alps, and which 

 are required for the pollination of the flowers and the 

 fertilisation of the ovules. That the number of insects 

 which could assist in cross-pollination is small in the 

 Alps is undoubted ; though Dr. Joly states that numbers 

 are attracted to the glaciers and snowfields in the dusk 

 by the reflected light, and perish there in large numbers. 

 But a doubt is raised as to whether this is the true expla- 

 nation of the beauty of the alpine flora, from the fact 

 that a comparatively small number of alpine plants are 

 dependent on the ripening of the seeds for their pro- 

 pagation. 



