GROUPS OF PLANTS. 



13 



Diatoms constitute a large group of unicellular plants, oc-- 

 curring in both fresh and salt waters. They form the plankton or 

 floating microscopic life found in oceans and lakes, which is the 



Fig. 9. Some common marine algas. i, Lamiftaria, showing portions of three leaf- 

 like thalli and holdfast; 2, dichotomously branching thallus of Fucus; 3, Sargassum, or 

 "gulf weed," showing a thallus resembling a leafy branch, with swollen, beiry-like air 

 bladders, which act as floats; 4, Dasya, a delicate branching filamentous seaweed, 

 attached to a blade of eel-grass; s, dichotomously branching thallus of Chondrus, or Irish 

 moss; 6, Leaf-like thallus of Grinnellia; 7, densely, but delicately branched thallus of 

 Polysiphonia. i, 2, 3 are Brown Algae and 4, S, 6, 7 are Red Algse. 



