446 The Living Plant 



latter bear a striking, albeit superficial, resemblance to those 

 parts in the higher land plants. Whatever their shapes, they 

 exhibit a wide prevalence of minuteness, thinness, or fine division 

 of structure, these features being correlated with the comparative 

 scarcity of the indispensable gases, which they, like the fishes, 

 must take from solution in the water. In color they are typically 

 green from the presence of chlorophyll, by aid of which they make 

 their own food precisely in the manner of the familiar green land 

 plants; but in a good many kinds, including most of the larger 

 and best-known, the green is mixed up with red or brown pig- 

 ments which aid in a better utilization of the light under the con- 

 ditions prevailing where those kinds make their homes. Their 

 anatomical structure is cellular, as in land plants, but much 

 simpler, with far less division of labor among the various cells, 

 and only unimportant structural differences between the several 

 tissues. Their reproduction is partly by fission, but chiefly by 

 spores, which are simple one-celled bodies various in aspect and 

 mode of formation, some of them actively free-swimming, and 

 others passively floated by currents of water; in addition, fertiliza- 

 tion occurs, in all grades of complexity from the accidental fusion 

 of two precisely-similar free-swimming cells up to the union of a 

 tiny, free-swimming, chemotropically-attracted, male cell with a 

 sessile food-filled female cell. 



The best-known kinds of the Algae are these. Among the 

 GREEN (AND BLUE-GREEN) ALGAE are the Diatoms, found in all 

 waters, with microscopical flinty shells of wonderful beauty and 

 marvelous variety; the Blue-green kinds, forming unhealthy- 

 looking scums of that color in unpleasant damp places; Pleuro- 

 coccus, which makes up the familiar green coating upon the shaded 

 sides of standing tree-trunks; Vaucheria, the darker-green coating 

 on damp earth in warm shaded places; Uroglcena, hardly visible to 

 sight, which gives the bad odors and taste to the water of reser- 

 voirs, from which, fortunately, it can be driven by traces of com- 

 pounds of copper; Spirogyra, which composes the very bright green 



