308 THE SIMPLEST GREEN PLANTS 
sulphate in the water kills the plants without making the 
water unsafe for drinking purposes. A canvas bag contain¬ 
ing crystals of copper sulphate is dragged through the water 
by men in a row boat. 
SUMMARY 
Both pleurococcus and spirogyra are called algae, and 
each' is typical of many other plants of the same kind. 
Our chief interests in them are that they are adapted to 
very simple conditions for living, and that each cell is 
capable of carrying on all the life processes for itself. Plants 
like pleurococcus are called unicellular; those like spirogyra, 
which consist of many cells joined end to end thus forming a 
strand, are called filamentous algae. Pleurococcus is found 
on old buildings, fences, posts, rocks, and on the bark of 
trees. It shows more plainly in wet weather than in dry, 
for then it is growing. Spirogyra grows in running water, 
attached to objects on the bottom, or floats in masses on the 
surface of ponds, ditches, and sluggish streams. Neither 
of these plants has any economic value, but some algae cause 
drinking water to have an unpleasant taste and smell. 
Algae are simple plants which grow in water or in moist 
places. Fresh-water algae are usually small. Algae illus¬ 
trate how a plant cell carries on the life processes. . The 
cell is the unit of plant structure, and plant cells are similar 
to animal cells in all essential respects. 
QUESTIONS 
What is a cell? Compare plant with animal cells. Explain the 
process of conjugation. In what respects is the formation of a zygospore 
similar to the process of fertilization in a flowering plant? 
REFERENCES 
Atkinson, High School Botany. 
Bennett and Murray, Cryptogamic Botany. 
Bergen and Caldwell, Practical Botany. 
Leavitt, Outlines of Botany. 
