THE ALG^E 215 



Such is the simple history of Nostoc. Neither in this 

 genus nor in any of the blue-green Algae has any kind 

 of sexual reproduction been observed. The plants of 

 this class must rank, according to our present know- 

 ledge, as among the lowest members of the vegetable 

 kingdom, the only others which are equally simple 

 being the Bacteria (to be subsequently described), some 

 of which appear to be closely allied to the Cyanophyceae. 



