110 TAXONOMY 



thickness in different species, being the same diameter at 

 apex and base. Reproduction takes place by means of gonidia, 

 which are round and arise directly from the vegetative cell. 

 This genus is called Leptothrix by Kiitzing and Steptothrix 

 by Cohn. 



Genus : Crenothrix Cohn. 



The cells are united together into filaments which are un- 

 branched. The filaments gradually enlarge toward the free 

 end, thus making a distinction between the apex and base. 

 The sheath which covers the filaments is thick and often 

 becomes infiltrated with the hydroxide of iron after being 

 cast off in water in w r hich there is a large amount of iron. 

 Reproduction takes place by the formation of round gonidia 

 which are formed in the beginning by division perpendicular 

 to the long axis of the cell and later by division in three direc- 

 tions of space. Only one or possibly two species can be 

 placed in this genus. 



Genus : Phragmidiothrix Engler. 



The cells in the beginning form unbranched threads. Cell 

 division takes place in three directions of space, thus forming 

 within the sheath a mass of cells. Later these cells may 

 burst through, multiply, and form branches after acquiring 

 sheaths. The sheath in this genus is quite thin and can 

 scarcely be seen. 



