308 



THALLOPHYTES 



one of the simplest of the Green Algae. It forms green coatings, 

 resembling green paint, on flower pots, damp earth or walls, and 

 on the trunks of trees. It is a single, globu- 

 lar, non-motile cell. It has a definite w^all, 

 a large lobed chloroplast suggesting several 

 chloroplasts, and its nucleus and cytoplasm 

 are well defined. It reproduces entirely by 

 cell division, thus forming no zoospores or 

 gametes. They are small plants and a mass 

 of them perceptil)le to the eye consists of 

 numerous individuals. They divide rapidly 

 when conditions are favorable, and daughter 

 cells recently formed and not yet separated 

 are usually seen when a mass of individuals 

 is observed with the microscope. 



Scenedesmus. — This form, which is 

 common in fresh water, is often classed with 

 the Protococcales. The individuals form 

 simple colonies with the individuals usually 

 arranged in a row as shown in Figure 263. There are no zoospores 



Fig. 263. — Scene- 

 desmus. Above, a 

 colony of Scenedesmus 

 quadricanda consisting 

 of four cells arranged 

 in a row; below, a cell 

 of the old colony form- 

 ing a new colony. 

 X 600. Drawn from 

 West. 



Fig. 264. — Pediaslrum horyanum. At the left, the plate-like colony of 

 cells, some of which have formed zoospores and from one of which the 

 zoospores are escaping; at the right, zoospores arranging themselves into 

 a new colony. X about 400. From Braun. 



or gametes, but reproduction is effected by the division of each 

 cell into daughter cells which escape as a new colony. 



