202 BOTANY 
plants, and that they are poor in lime, potash and 
phosphorus. The water of a bog, too, is strongly acid, 
and as arule much colder than that of a swamp. The 
acid character is due doubtless to the absence of lime. 
Thus bog societies, though growing where water is 
plentiful, are of an entirely different character from 
those of the swamp. The plants of such societies are 
rather xerophytic in character. They have a diminished 
L. Cockayne, Ph.D., F.R.S., photo 
Bog, Stewart Island—chiefly umbrella fern. 
power of root absorption and must therefore provide 
against excessive transpiration. Several reasons have 
been assigned for this peculiarity, none of which is 
entirely satisfactory. It is said, for instance, that the 
excessive coldness of bog water tends to check absorp- 
tion, while it is also alleged that the presence of acids 
and certain mineral salts has a similar effect. In the 
true. bog, bog-moss or sphagnum as a rule forms the 
basis of the plant society. This is by some said to be 
due to the fact that sphagnum, unlike most plants, 
