THE ALGAE 109 



When the colony is mature akinetes may be formed from any or all of 

 the vegetative cells, and it is not unusual to find all the cells between two 

 heterocysts converted into akinetes. Each germinates to form a new trichome. 



While many species grow on bare soil among mosses, others are sub- 

 terranean, and have been found as much as three feet deep in the soil. Many 

 are aquatic and live free-floating, attached to vegetation or on the bottom of 

 the pond. A few species favour running water, particularly fast-flowing 

 mountain streams. 



Nostoc frequently forms the algal component of Lichens {e.g., Peltigera 

 canina, see p. 369), while one species is found in symbiotic association with 

 Anthoceros (see p. 409). 



