220 INTRODUCTION TO BOTANY 
The bluish-green balls (fig. 172, 4) of Nostoe plants are 
found upon damp soil or floating upon stagnant water. Under 
magnification! the Nostoc ball is seen to be composed of 
Fic. 172. Nostoc 
At the left (1) are several of the osfoc balls, 
which appear as glistening, rounded masses (nat- 
ural size). At the right (B), inclosed in gelatinous 
material, are a few chains of Vostoc plants which 
have been taken from one of the balls and greatly 
magnified. In the chains several of the enlarged 
heterocysts may be seen 
granular jelly, imter- 
woven by many chains 
of cells, each of which 
is a Wostoe plant (fig. 
172, B). These chains 
often divide into two 
or more shorter chains, 
breaking where there 
are large, dead cells 
(heterocysts), and each 
chain proceeds to live 
as a new plant. Nos- 
toe may absorb the 
materials needed for 
photosynthesis directly 
through the cell walls, 
or it may perhaps ab- 
sorb organized foods as 
do the bacteria, since 
much food of this kind 
is present in the water 
in which the plants live. 
In times of drought the 
jelly balls dry slowly 
and may become dry 
enough to erumble eas- 
ily, but when a favora- 
ble amount of moisture 
returns, the plants within the ball may proceed to grow. 
1 When beginning the study of the algie it is often better to use a good 
specimen under a. demonstration microscope than to attempt individual 
microscopic work. If preceded by preliminary demonstration work the fol- 
lowing individual studies will be more intelligible and successful. 
