15] VEGETATIONAL TYPES OP FRESH WATERS 49I 



such surface inhabitants, according to Professor G. W. Prescott (in 

 lift.) ' some organisms are embedded in ice '. 



Whereas the majority of recognized land cryophytes belong to the 

 Green Algae — even when they are red, yellow, or brownish in actual 

 colour — or in several cases to the Cyanophyceae or Bacillariophyceae, 

 some Fungi and Bacteria may be associated as parasites. A few moss 

 protonemata have also been found growing on snow or ice, but with- 

 out developing into leafy plants. The numerous viable but quiescent 

 spores of airborne Bacteria, Fungi, etc., and tufts or scraps of Mosses 

 or other ' land ' plants, that are often present on the surface of old 

 snow and ice, can scarcely be considered as elements of its vegetation.^ 



It is on the floating sea-ice of boreal and austral regions, however, 

 that the most plentiful cryovegetation (of a sort) is commonly de- 

 veloped. Here Diatoms, particularly, are often abundant in the pools 

 that result from summer melting, frequently forming considerable 

 aggregations that render the surface brownish ; they also occur on 

 the sides and undersurfaces of the floes. Already before the end of 

 the last century, Nansen [Farthest North, I, pp. 444-5, 1897) reported 

 from the North Polar Basin : 



* one-celled lumps of viscous matter, teeming in thousands and millions, 

 on nearly every single floe. . . . When the sun's rays had . . . melted 

 the snow, so that pools were formed, there was soon to be seen at the 

 bottom of these pools small yellowish-brown spots. . . . Day by day 

 they increased in size, and absorbing . . . the heat of the sun's rays, 

 they gradually melted the underlying ice and formed round cavities, 

 often several inches deep. These brown spots were . . . algae and 

 diatoms. They developed speedily in the summer light, and would 

 fill the bottoms of the cavities with a thick layer . . . the water also 

 teemed with swarms of animalcules . . . which subsisted on the plants. 

 I actuallv found bacteria. . . .' 



Benthos 



The vascular plants of semi-aquatic marginal communities have 

 been dealt with earlier in this work and those that comprise the main 

 serai stages of shallow waters are discussed later in the present 

 chapter. Here we must concentrate upon the usually smaller, 

 attached or loose ' bottom ' forms of Algae and other organisms which 

 comprise the benthos. For, altogether, these make up a substantial 



^ It is not thought that the Hving Moss tussock found drifting on an ice-island 

 near the North Pole (p. 109) actually grew on the ice, but this seems possible. 



