382 SCIENCE PROGRESS 



on this organism which bear out the accurac}' of this state- 

 ment (fig.4,E). As will be seen below, the same cellular struc- 

 ture of the sheath holds good for Cladothrix dichotoma. Garrett 

 further alludes to another characteristic of Crenothrix that is 

 very remarkable. He states that when the cocci are massed 

 together in a common mucilaginous envelope after extrusion 

 from the sheath, the further development is effected by numbers 

 of these cocci forming themselves into line, each line becoming 

 presumably a new Crenothrix thread. It is far more probable 

 that each thread is formed by the growth of a single coccus, 

 but at the same time during its period of phenomenal activity 

 we must expect unusual peculiarities of growth. The statement 

 at any rate demands confirmation. Searchers after Crenothrix 

 polyspora will have a little difficulty in distinguishing young 

 Crenothrix from young Cladothrix threads. The identification 

 is considerably facilitated by noting the fact that, as seen in 

 Plate IV, the individual cells of Crenothrix are distinguish- 

 able without staining. The cells of Cladothrix do not become 

 individually distinguishable without subjecting the threads to 

 the action of appropriate staining reagents. 



Cladothrix dichotoma (Cohn) 



This organism consists of long thin threads attached at one 

 end to various objects at the bottom and sides of stagnant 

 streams. Like Crenothrix each thread is made up of a number 

 of rods enclosed by a common sheath, but unlike Crenothrix 

 the rods are always in single rows, are of uniform length in 

 each thread, and usually longer and thinner. Also, except in 

 rare cases, the threads are uniform in thickness. Each rod 

 measures from 3 \x to 6 p in length with a width of approximately 

 2 fi. A representation is given in Plate V and fig. 5. Occa- 

 sionally the threads appear as if branched. This is due to 

 the fact that some of the rods slip out laterally through the 

 sheath and develop into new threads without severing their 

 connection with the parent plant. This gives the appear- 

 ance of dichotomous branching, and has given the name to the 

 organism, but in the writer's experience this false dichotomous 

 branching only rarely takes place. When stained with iodine 

 the rods become visible. Each one possesses a distinct cell 

 membrane. The sheath is formed by a contribution from 



