AQUATIC PLANTS OF FRESHWATER 



or in the heated water of a boiling spring. They are the last vestige of 

 life in the region of perpetual snow or in the heated basin of the geyser. 

 The numerous forms are to be found in every stagnant pool and ditch, 

 rivulets,' springs and in all other bodies of water. In pools and ponds the 

 most conspicuous forms are Oscillatoriae and Zygnemaciae; the former 

 forming dense floating or attached slimy strata, having fine rays extending 

 from the mass, of dark green, purplish or bluish-black color. The 

 Zygnemae are bright green filamentous masses, usually entangled among 

 the water plants, twigs, etc. When in fruit they become dingy, yellowish, 

 or dirty looking. Late in the season Rivulareae and Nostocs are often 

 met with. These adhere to larger plants and floating matter and form 

 fine fringes around the stems and edges of the leaves, or little green and 

 brownish globules and small protuberances. Of the river Algae, the 

 Desmids are abundant in the spring and summer months, adhering to 

 rocks and water plants; and Chsetophora, Scytonema and Palmela are also 

 numerous, often free but sometimes attached to objects in the water. 



Diatoms are also classed in the family of Algae and consist of minute 

 silicious organisms which were formerly considered as belonging to the 

 lowest forms of animal life. They are a higher form of Algae and obtain 

 firmness by depositions of silica. Another class, the Acetabulariae, deposit 

 carbonate of lime. 



The mentioned Algae and Confervae are those with which the aquariist 

 becomes familiar, the group being too complex in classification for further 

 description in a work of this character. The common small aquarium 

 species are mentioned elsewhere as they have more or less parasitic character. 



Algas have many useful purposes in the aquarium, as they form a 

 screen on the glass to intense light, serve as a natural food for both the 

 fishes and the scavengers, and have beneficial medicinal properties to fishes. 

 When the growth is of a clear green color and not so thick as to be un- 

 sightly, it may be left undisturbed on the glass or removed only from the 

 side through which the contents are viewed; but when the growth, both 

 on the glass and in the water, assumes a brown color, it is indicative of 

 a dead and decaying condition and it is advisable to thoroughly clean the 

 aquarium and refill with fresh water, as the appearance of the algae is a 

 good indication of the water conditions. Excessive growth on the plants 

 is injurious and they should be cleaned to prevent suffocation or the 

 afi^ected leaves removed, but usually the fishes and scavengers, when not 

 overfed, keep them sufficiently clean. It is for'^this purpose that gold- 

 fishes are kept in tanks with aquatic plants by florists, to keep down both 

 objectional plant and injurious insect life. 



Should the growth become so excessive as to destroy the lower leaves 



Z07 



