166 Proceedings of the Royal Iviah Academy. 



in robbing the dead and decaying parts of themselves of this 

 liquid. 



It might be supposed, too, that the decay of the vegetation, 

 although at best only partial in peat, would give rise to substances 

 which would dissolve in the excess of water, and exert an influence 

 osmotically, similar to what is known to be the case in salt marshes. 

 Schimper,^ in fact, emphasizes the point that in the very sour humus 

 of bogs the vegetation assumes a distinctly xerophytic character 

 because the humus acids hinder the absorption of water by the roots. 



Livingston,^ on the other hand, has recently shown that the 

 osmotic pressure of bog-water, as determined by the freezing-point 

 method, shows almost no increase in amount over that of ordinary 

 lake or river water. He concludes that it must be the chemical nature 

 of the very small amounts of dissolved substances in bog-waters 

 which prevents ordinary swamp-plants from growing in them. This, 

 of course, does not explain the xerophytism of our bog-plants ; but if 

 this view is correct, neither can we explain it by the assumption of 

 the presence of osmotically active soluble humus compounds in the 

 bog-water. 



Lastly, it must be remembered that at times in the summer 

 the surface-layers of such a bog may become very dry, so that one 

 may walk dry-shod over it, and hence provision on the part of the 

 plants against such periods is necessary. The whole question, how- 

 ever, is one on which more information is wanted.^ 



llie Eriophorum Association. (E.) 



Though both species of cotton-grass are almost always present in 

 small quantities throughout the moorland, it is only occasionally, and 

 at high altitudes, that they become dominant. We surveyed many 

 square miles of mountain, tenanted by the Calluna and Scirpiis associa- 

 tions, before we found any trace of what might be fairly described as 

 Eriophorum-mooY. From the map it will be seen that this type of 

 vegetation is rare on the hills ; quite the best example of it is a large 

 patch of sloping deep bog above the butts of the main Kilbride rifle- 

 range (2364 feet downwards). Here the ground presents a waving surface 



^ Schimper, " Pflanzengeographie," 1898, p. 124. 



2 Livingston, "Physical Properties of Bog-Water," Eot. Gazette, xxxvii., 

 p. 383, 1904. Ref. in Bot. Centralblatt, 96, p. 269, 1904. 



^ For a discussion of the xerophytic characters of these plants, see Warming, 

 *' Pflanzengeographie," 1896, p. 174 



