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. Chondrus crispus: A, B, C, D, various forms of thallus; H, holdfast; F, spor- 

 angia; T, transverse section of thallus shov.ing epidermis (E), sporangium with spores (F) ; 

 S, spores separated in glycerin preparation of thallus by pressure on the cover glass. The 

 spores occur in groups of fovir (tetraspores) and the tetrad group is about 30 /i in diameter. 



