THE ALG^E 147 



the other hand, the simplest Algae consist of single 

 isolated cells. Amid this vast range of forms it is 

 evident that only a very few types can be dealt with 

 here. As far as possible, our examples are selected with 

 a view to illustrate the most striking variations in the 

 life-history and mode of reproduction of Algae. 



The classification of the Algae into their principal 

 classes roughly follows the colour not that colour is in 

 itself of systematic importance; it happens, however, among 

 these plants that differences in their pigments generally 

 coincide with important morphological distinctions. We 

 will begin with the pure green Algae, those, namely, in 

 which the chlorophyll, like that of most of the higher 

 plants, is not disguised by the presence of any other 

 colouring matter. This class the Chloropliycece in- 

 cludes the majority of the fresh-water Algae, as well as 

 many Seaweeds. They are, on the whole, among the 

 simpler Algae, and many of the unicellular forms belong 

 here ; but simple as they are in structure, some of them 

 in their mode of development approach nearer to the 

 higher plants than any other Algae. We will take as 

 our first type a fresh-water Alga which, though anatomi- 

 cally simple, shows a very high form of reproduction. 



A, THE CHLOKOPHYCE.E 



TYPE IX. (EDOGONIUM 

 1. STRUCTURE 



The genus (Edogonium, of which there are a great 

 many species, includes some of the commonest fresh- 

 water Algae, and may be found in almost any pond or 



