146 Aquatic Organisms 



and many others are stragglers from large dry land 

 groups. That readaptation to aquatic life has occurred 

 many times independently is indicated by the fact that 

 the more truly aquatic families are small and highly 

 specialized, and are widely separated systematically. 



Bryophytes — Both liverworts and mosses are found 

 in our inland waters, though the former are but spar- 

 ingly represented. Two simple Riccias, half an inch long 

 when grown, are the liverworts most commonly found. 

 One, Ricciafluitans, grows in loose clusters of fiat slender 

 forking sprays that drift about so freely that fragments 

 are often taken in pond and river plancton. The larger 

 imbroken more or less spherical masses of sprays are found 

 rolling with the waves upon the shores of muddy ponds. 

 The other, Ricciocarpus natans, has larger and thicker 

 sprays of green and purple hue, that float singly upon the 

 surface, or gather in floating masses covering considerable 

 areas of quiet water. They are not uncommonly found in 

 springtime about the edges of muddy ponds. Under- 

 neath the flat plant body there is a dense brush of 

 flattened scales. 



Water mosses are more important. The most 

 remarkable of these are the bog mosses {Sphagnum). 

 These cover large areas of the earth's surface, especially 

 in northern regions, where they chiefly compose the 

 thick soft carpet of vegetation that overspreads open 

 bogs and coniferous swamps. They are of a light grey- 

 green color, often red or pink at the tips. These 

 mosses do not grow submerged, but they hold immense 

 quantities of water in their reservoir cells, and are able 

 to absorb water readily from a moist atmosphere; so 

 they are always wet. Supported on a framework of 

 entangled rootstocks of other higher plants, the bog 

 mosses extend out over the edges of ponds in floating 

 mats, which sink under one's weight beneath the water 



