634 Professor L. G. Miall, [Feb. 18, 



centre being occupied by an abundant pith of star-shaped cells, 

 which entangle much air. 



The Hair moss (Polytrichum commune) of the moor has a delence 

 against sun and wind, which has been described by Kerner. The 

 leaf has wings, like an altar piece, which can open and shut. The 

 assimilating surface occupies the centre, and rises into many green 

 columns. In wet or cloudy weather the wings open wide, but when 

 the sun shines they fold over the columns, and protect them from 

 scorching. 



All the most characteristic plants of the moors are Arctic, 1-ing, 

 bilberry, crowberry, certain rushes, Nardus, Festuca ovina, most of 

 our club mosses, the hair moss and Sphagnum range withm the 



Fig. 11. — Transverse section of leaf of Aira Jtexnosd. 



Arctic circle; while the large-flowered heaths get close up to it. 

 Most of them are found on both sides of the Atlantic, and some, like 

 the crowberry and Festuca ovina, have a singularly wide distribu- 

 tion. 



It has often been pointed out that great elevation above sea level 

 produces a similar effect upon the flora to that of high latitude. In 

 the Alps, the Pyrenees, the Himalayas, and even in the Andes, the 

 forms characteristic of northern lands reappear, or are represented 

 by allied species. Where, as in the case of the Andes, nearly all the 

 species differ, it is hard to draw useful conclusions, but whenever the 

 very same species occur across a wide interval the case is instructive'. 

 In the Alps we find our moorland and Arctic flora almost complete, 

 though Eubus Chamsemorns, Erica Tetralix, and E. cinerea (both 



