408 X. GENEEAL REMARKS. 



So likewise in North Britain some plants occur in the 

 ascending stage of altitude, between 200 and 700 yards, 

 which in England and Wales are found only above 700 

 yards ; for example, Salix herbacea and Carex rigida. 

 The decrease of height for the lower limits, arising out of 

 more northerly latitude, thus brings species into the same 

 ascending stage, if our view takes in the entire length of 

 Britain ; while a more limited view would correctly assign 

 them to different stages, and thus tend to augment the 

 discrepancies between the floras of different levels. 



In accordance with the decrease in the total flora, ver- 

 tical ascent will tend usually to decrease also the orders 

 and their included species. The number of orders repre- 

 sented in the three vertical stages is varied thus : — 

 Lowest, 98. Ascending, 77. Uppermost, 47. 

 Saxifragacece is the only order which exhibits an absolute 

 increase of species in the uppermost stage; and the excess 

 is one of a single species only over the numbers found in 

 the two lower stages. Coniferce rise to four sj^ecies in the 

 middle stage, compared with three in the others ; this 

 excess being explained by the occurrence of Taxus baccata 

 above 200 yards, and of Junipenis nana below 700 yards; 

 although these two conifers do not seem to glow actually 

 on the same level. Melanthiacece are equal in the three 

 stages ; Tqfieldia succeeding Colchicum. All the other 

 orders (excepting some of those of a solitary species each) 

 show a decrease in number of species in one or other of 

 the higher stages ; the decrease being slower or more 

 rapid, greater or less, among the various orders, one com- 

 pared with another, as exhibited in the tabular list of 

 them on pages 362 to 364. 



But as in the case of latitude, still more so in that of 

 altitude, the absolute decrease of numbers in certain 



