220 



INTRODUCTION TO BOTANY 



The bluish-green balls (fig. 172, A) of Nostoc plants are 

 found upon damp soil or floating upon stagnant water. Under 

 magnification l the Nostoc ball is seen to be composed of 



granular jelly, inter- 

 woven by many chains 

 of cells, each of which 

 is a Nostoc plant (fig. 

 172, #). These chains 

 often divide into two 

 or more shorter chains, 

 breaking where there 

 are large, dead cells 

 (Jieterocystsy, and each 

 chain proceeds to live 

 ;v. as a new plant. Nos- 



toc may absorb the 

 ":\::: , materials needed for 

 r^'vv photosynthesis directly 

 ':[;;. through the cell walls, 

 ^ !! or it may perhaps ab- 

 ^;v).v' sorb organized foods as 

 do the bacteria, since 

 B much food of this kind 



is present in the water 

 in which the plants live. 

 In times of drought the 



At the left (A) are several of the Nostoc balls, -jellv balls drv slowly 

 which appear as glistening, rounded masses (nat- J ^ J k J 



ural size). At the right (B), inclosed in gelatinous 

 material, are a few chains of Nostoc plants which 

 have been taken from one of the balls and greatly 

 magnified. In the chains several of the enlarged 

 heterocysts may be seen 



FIG. 172. Nostoc 



and may become dry 

 enough to crumble 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 algse 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. 



