SIMPLER PLANTS AND ANIMALS 



filaments are branched, forming a tuft attached to stones, but 

 they have no structure comparable to a root. Many algse 

 are single-celled ; such are the desmids and diatoms although 

 the constriction around the center of desmids makes them look 

 two-celled, and many diatom cells cling together in spherical 

 and ribbonlike colonies. Marine algas such as the familiar 

 seaweeds are conspicuously red or purplish or brown; but ex- 

 cept for the diatoms most of the fresh-water algae are green or 

 blue-green. In all alg£e the cells contain chlorophyll, the green 

 substance by which plants are able to prepare their own food 

 out of the raw materials of non-living matter. In green algae 

 masses of chlorophyll are naked within the cells displaying the 

 characteristic green color, but in the diatoms the chlorophyll 

 is cloaked with yellowish-brown diatomin, which gives diatoms 

 their typical color. Fresh water algas grow in untold numbers 

 in running streams of every description, in lakes, ponds, and 

 pools, and in every little place which holds a few days' stand 

 of soft water. 



Six classes of algas are commonly recognized. They are 

 known chiefly by their colors, red or brown, or green; these 

 colors except in the green algae are due to coloring matter 

 which covers the green chlorophyll. Two of these classes are 

 predominantly marine, and the members of one, the yellow- 

 green algae, are not common or conspicuous enough to be de- 

 scribed here. 



1. Blue-green; filamentous algae, Cyanophycece. Alostly 

 in fresh water. 



2. Green; filamentous algas, desmids, stoneworts, Chlo- 

 rophycecB. In fresh and salt water. 



3. Yellow-green; Bacillariacece. Mostly in fresh water. 



4. Diatoms, Diatomacece. In fresh and salt water. 



5. Brown; brown seaweeds, PhceophycecB. Mostly in 

 salt water. 



6. Red; red seaweeds, Rhodophycece. Mostly in salt 

 water. 



47' 



