ECONOMIC IMPORTANCE OF ALGM 
307 
cell. Thus there is formed a single roundish mass of proto¬ 
plasm surrounded by a thick wall. This mass of protoplasm 
is called a sexual spore, because two cells unite to form it. 
The two cells which thus unite are called gametes and are 
identical in all their parts. This spore, therefore, is known 
as a zygospore (Greek, zygos, yoke; spora , seed). In the 
formation of a zygospore, the cells are joined permanently and 
a simple form of sexual reproduction is present. 
As a zygospore, spirogyra can live in a resting condition 
during periods unfavorable to its growth, as in winter or 
during a drought. When conditions again become favor¬ 
able the zygospore germinates and grows into a filament. 
The spirogyra is able to do the same things which a pleuro- 
coccus does and has the same life processes. 
LABORATORY STUDY OF SPIROGYRA 
Notice: (1) the clear outer part called the cell wall; (2) the main 
mass of the cell, a substance called cytoplasm. (This can be easily seen 
by putting a 5 per cent sugar solution under the cover glass. The cyto¬ 
plasm draws away from the cell wall into a compact mass in the center 
of the cell.) (3) The darker portion, the nucleus, in or near the center of 
the cell. (This can be clearly seen by putting a drop of weak iodine 
under the cover glass, using fresh material for this test.) (4) A spiral 
band of green coloring matter, chlorophyll, containing bright spots. 
Examine spirogyra in a mass, floated out in water in a glass or on a 
plate. Feel it and observe that it is slimy. Note its color and deli¬ 
cacy. After it has been in the sun for a time, note the bubbles of gas 
entangled in the spirogyra, which help to make it float. With a micro¬ 
scope examine filaments which are joined in places by outgrowths from 
other filaments. Such filaments are said to be in conjugation. Draw 
the outgrowing tubes, the empty cell, and the zygospore or zygote. 
Label all. 
263. Economic Importance of Algae. — Although algae are 
so small they sometimes make trouble by causing the water 
stored in reservoirs to have a fishy taste and smell. This 
is due to substances formed during their rapid growth, not 
harmful, but unpleasant. A very small quantity of copper 
