THE ALG 69 
most colorless jelly are seen chains of cells, each chain 
being a Nostoc plant. What is the form of a cell? How 
are they related to one another? Have different chains 
similar lengths? Are all the cells of different plants of 
similar size and structure? 
Reproduction. How does a plant consisting of a few 
cells become one consisting of many cells? Does this result 
directly in the production of new plants? In very long 
plants the large cell—the heterocyst—is usually not at the 
end of the chain, as is the case in the very short plants. 
Can you find how this fact is related to the reproduction of 
the Nostoe plants? 
Make drawings and notes descriptive of this plant. 
General questions.—Is Nostoc a more or less complex 
plant than Pleurococcus? How do the plants differ in 
structure and in general appearance? What differences in 
their reproduction? Of what advantage to Nostoc is the 
jelly surrounding it? 
Nostoc usually lives in regions where there is consider- 
able decaying organic matter. It probably uses some of this 
as nourishment. Plants that do not use these organic sub- 
stances for food must make their food in some other way. 
To do this they must have the green coloring-matter—chlo- 
rophyll—which, when the sunlight falls upon it, enables 
these green plants to construct their own food materials. 
These food materials are then used by the plant in its 
growth and in the repair of old parts, just as Nostoc uses the 
organic substances it does not make for itself. Nostoc has 
some chlorophyll, though not so much as the Pleurococcus. 
This indicates that Nostoc plants either can not grow as rap- 
idly as Pleurococcus plants, or that they obtain more of their 
food already made. In Nostoe the chlorophyll is mixed 
with a blue coloring-matter. 
