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 
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. 
on the trunks of trees. It is a single, globu- 
lar, non-motile cell. It has a definite wall, 
a large lobed chloroplast suggesting several 
chloroplasts, and its nucleus and cytoplasm 
are well defined. It reproduces entirely by 
cell division, thus forming no zoéspores or 
gametes. They are small plants and a mass 
of them perceptible 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 268. There are no zoéspores 
CREO 
aN 
Fic. 264. — Pediastrum boryanum. At the left, the plate-like colony of 
cells, some of which have formed zodspores and from one of which the 
zoéspores are escaping; at the right, zodspores arranging themselves into 
anew 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. 
