458 HIGHER FISSION-FUNGI. 



all the forms previously discussed, and many investigators 

 consider them as true algae. On the other side, the con- 

 nection with the simple fission-fungi is still so close that 

 at least a brief mention seems necessary. 



In distinction to the true bacteria, the members of this 

 group have this in common, that the threads can be recog- 

 nized as having a basal (not growing, often attached) and 

 an apical (growing, free) end. 1 The ends are often of 

 different thickness. 



Key to the Recognition of Some of the More Impor- 

 tant Genera of Fission-algae. 



Threads without distinct sheaths : 



(a) Without sulphur granules. Leptothrix Kiitzing, see below. 



(b) With sulphur granules, motile, not attached. Beggiatoa Tre- 

 visan, page 461. 



Threads with sheaths : 



(a) Without sulphur granules. 



1. Without pseudodichotomous branching. Crenothrix Cohn, page 

 463. 



2. With pseudodichotomous branching. Cladothrix Cohn, page 

 465. 



(b) With sulphur granules. Thiothrix Winogradsky. 



Leptothrix epidermidis Biz. 2 



(Plate 69.) 



Microscopic Appearance. — In our preparations there 

 are sturdy unbranched threads, distinctly jointed and 

 readily falling apart, with no evident distinction as to base 

 and apex. Young cultures show bacilli about like the B. 

 mesentericus (69, xi and xn). 



Motility. — The young rods present distinct motion like 

 that of bacilli. We were unable to stain flagella. 



Staining Properties. — Stains with all anilin dyes and 

 by Gram's method. With iodin and iodid of potassium 

 alone there is no blue stain. 



1 We must certainly admit that the discernment of the two ends 

 has often caused greater trouble than was to be expected from the 

 statements of Blicher, for example, in the case of Beggiatoa. 



2 Before the leptothrix of the mouth had been cultivated we could 

 place the L. epidermidis among the ' ' true ' ' leptothrices only with 

 reservation. (See p. 461.) 



