264 FLORA OF THE WEST YORKSHIRE HILLS. 



As the two sections differ widely in their formation and aspect, 

 it follows naturally, from what has already been stated with respect 

 to the joint influence of elevation, moisture, and soil on plant 

 distribution, that an expression of this difference should be found 

 in their flora. That this is the case is proved by facts, but it is 

 not the writer's intention in the present paper to adduce the 

 minute particulars necessary to establish them. 



The most careless and indifferent observer must at one time or 

 another have been struck with the great number and variety of 

 plants growing on low-lying plains, and had his attention drawn to 

 the prodigal floral display induced by the warmth of the sun and 

 favourable conditions of soil and situation. If he quits the plain 

 and begins to climb a lofty hill, he will find that the plants made 

 familiar to him by their very abundance, if not known by name 

 first of all become less numerous, both as regards species and 

 individuals, and then drop out altogether, some at one level and 

 some at another. Thus, on the Yorkshire hills, after reaching 

 nine hundred feet, he would no longer see Dogwood and Rha^n- 

 nus, and hawthorn would be scarce. He would find that the cul- 

 tivation of field crops, vegetables, and fruit-trees ceases practically 

 at eleven hundred feet ; that bracken, so plentiful on the slopes 

 between twelve hundred and seventeen hundred feet, completely 

 disappears above eighteen hundred feet, at which height, also, the 

 only trees are stunted specimens of mountain ash, birch, juniper, 

 and hazel ; at nineteen hundred feet the cross-leaved heath 

 becomes uncommon ; and above two thousand feet only ling is 

 conspicuous. 



It must not be imagined, however, that this process of elimi- 

 nation goes on without compensation ; new species appear to take 

 the place of those which become eliminated. At first, the new 

 members of the flora are somewhat scarce, but they become more 

 numerous as the elevation increases, though they never equal, 

 either in variety or number, the plants whose places they have 

 taken, and they find their most congenial home at or near the 

 windswept summits of our loftiest hills. 



Many causes combine to favour, on the one hand, the ascent 

 of the lowland types, and on the other the descent of the moun- 

 tain forms. It cannot, however, be said that, because a certain 



