CHAPTER II 

 AQUATIC VEGETATION 



AQUATIC vegetation includes both salt and fresh - water 

 forms. These two groups are connected by the plants, 

 few in number, belonging to brackish water, which is found at 

 the mouths of rivers, in salt marshes that are gradually being 

 reclaimed, and in inland saline lakes. 



The flora of the sea, as distinct from that of the seashore 

 already described, consists mainly of Algae, red, green, and brown. 

 In fresh water the predominant plants are flowering, and only 

 the green Algae are usually found. In addition to flowering 

 plants, certain Mosses, some few Ferns, and other Cryptogams 

 occur in fresh water, but are absent in salt water. Among Mosses 

 may be mentioned some species of the Fern Moss (Hypnum), 

 and the Bog or Sphagnum : The Marsh Fern (Aspidium Thelypteris) , 

 the Pillwort, the Quillwort, and the Bog Equisetum are instances 

 of fresh-water Cryptogams ; these groups are entirely absent 

 from the sea flora. There is thus a striking difference in fresh- 

 water vegetation compared with marine. 



The flora of the seashore, with the exception of the Seaweeds, 

 is mainly terrestrial, not aquatic ; at the same time, it is profoundly 

 influenced by the sea, for the sea water bathes at every high 

 tide the belt of vegetation growing on the shores, and the spray, 

 containing salt, falls on the cliffs and gives salt-loving plants 

 some of the food material they require. The effect of this per- 

 petual motion of the waves on vegetation may be compared with 

 the effect of flowing water on fresh-water plants. The flora of 

 a stagnant pond is different from that of a stream or river. 

 Water in motion makes great demands on the resisting power 

 of plants ; in structure it will be seen that they have far more 

 highly developed strengthening tissue than those which merely float 

 on the surface of the water. 



