BRITISH 
FRESH-WATER ALGAi.* 
Alge are usually associated under five classes, which are 
taken in variable order, according to the judgment of the author, 
and may thus be enumerated :— 
I. CHLoropHyLLopayces, with the cell contents mostly of a 
chlorophyll green. 
II. Puycocnromorxyce4g, with the cell contents mostly of a 
bluish green. ; 
III. Meianopryces, with the cell contents olive, brownish, 
or blackish. 
IV. Ruonoruycesx, with the cell contents rosy, purple, 
crimson or violet. 
V. Diatomornycea, with an incombustible siliceous skeleton. 
Other arrangements have been proposed, but the above will answer for 
all practical purposes. The third class are all marine, and the majority 
of the fourth, so that, exclusive of Diatoms, which are a special study, 
the fresh water Alga are mainly included in the first two classes. 
Crass IL. CHLOROPHYLLOPHYCEA. 
Plants aquatic or aérial, one, or two, or many-celled, either 
single or associated in families. Either branched or simple. 
Cell wall not siliceous but combustible, sometimes composed of 
successive layers, or strata, of a gelatinous substance. Cell 
contents chlorophyllose, sometimes crimson, flesh-coloured or 
reddish-brown, often with a central or lateral nucleus. Starchy 
granules very rare. Vegetation by cell division. Fecundation 
often sexual. Propagation either by oospores or zygospores or 
gonidia, which are motionless or agile (zoogonidia).—Rabh. 
Alg. iii. p. 1. 
* Exclusive of Desmidiez and Diatomacez. 
