62 FLOWERS OF LAKES, RIVERS, ETC. 



like the first animals, undoubtedly arose from a liquid solution, plants 

 have been largely spread over the earth by water. 



There are certain plants like Hydrocharis, giving its name to this 

 type of Mora, which float on the surface, unattached, in fresh water, 

 swamp-plants, in still water, sailing about, and with erect stems and 

 leaves. Here, besides Frogbit, we may further include Bladderwort, 

 Duckweed, &c., and Water Violet. These plants have the same 

 specific gravity as the water. 



The shoots have long internodes, thin stems, stalkless or stalked 

 leaves, with threadlike segments, as in Bladderwort and Water Violet, 

 when submerged. Floating leaves are shield -shaped, egg-shaped, 

 heart-shaped, as in Hydrocharis, Lemna. and the division is well 

 shown in different types of Water Buttercup which have both types 

 of leaves. The plant is secured by its root. Nutriment is largely 

 absorbed by the stem and leaves. 



Many plants growing in water reproduce by division vegetatively, 

 as Frogbit and Duckweed. The pollination of the Frogbit, Water 

 Violet, and Bladderwort is effected by insects, and the Hornwort opens 

 its flowers under water. Frogbit and others are perennial, and survive 

 the winter by forming winter-buds or hibernacula, which sink in the 

 autumn and rise again in the spring. 



The plants that grow on the loose soil of aquatic formations where 

 the soil is quartz-sand are differentiated by the movement and salinity 

 of the water, and chiefly flowering plants grow upon it. The roots are 

 chiefly attachments, and the Mare's Tail has few or no root hairs, nor 

 has the \Vater Violet. Zostera forms meadows on account of its long, 

 creeping rhizomes or underground stems in purely saline waters, form- 

 ing maritime vegetation. Most maritime aquatic plants are Algae. 



Belonging to what is called the Enhalid formation are the colonies 

 of Zostera growing in salt water, and with Naias, unique amongst the 

 flowering plants, Ruppia and Zannichellia are found in brackish 

 water. In Zostera the leaves are ribbon-like and long, and the roots 

 rhizome-like. Along some shores it forms a regular zone. In brackish 

 water Ckara, Water Buttercup, Potamogeton, and Myriophyllum grow. 



The chief aquatic formations of flowering plants are known as the 

 Limneca formation, so called from the prevalence of the fresh-water 

 pond snail in it, and are submerged or have floating leaves. The chief 

 types belong to the Pondweed, Water Pepper, Bur-reed, Water Lilies, 

 Water Buttercup, Starwort, Water Celery, Sc. The Hydrophytes 

 altogether number some 700, of which we describe 41, and of the 

 Hydrophytes some 120 are lacustral. Here we include littoral, of 



