1912.] The Life-history of Cladothrix dichotoma (Cohn). 355 



the rod-like ciliated swarming cells, the method of cell division, the nature 

 of its reserve material, attest the fact that we cannot place Cladothrix 

 very far from the lower bacteria, particularly the genera Bacillus and 

 Pseudomonas. 



The connection with the genus Spirillum is also indicated by the occasional 

 thrusting forth of spiral cells or thread-fragments in all essentials identical 

 with those belonging to the genus Spirillum. 



In fact we see in Cladothrix a very good illustration of the fact that very 

 low down in the scale of organisation, organisms tend to approach more 

 closely in their affinities. It is in such widely distributed organisms as this 

 that such facts are best demonstrated. 



Summary. 



Distribution. — Widely distributed on the Continent, but not so in Great 

 Britain, its place being taken by members of the higher fungi. 



Occurrence. — Best growth found in ferruginous waters containing a slight 

 organic contamination. 



General Characteristics. — Long, colourless threads, 1-3 mm. long. Threads 

 may be free or attached, motile or non-motile. Tree-like colonies, exhibiting 

 false dichotomy, formed only when the water is almost or entirely motionless. 



Sheath. — Cells are enclosed in a sheath, which is soft and mucilaginous in the 

 young condition, but later hardens; it is ultimately split at the apex by the 

 growth of the enclosed cells, after which it remains permanently open. 

 The sheaths of motile threads do not harden, and consequently always 

 envelop the cells as a closely fitting sheath. Between the individual cells, 

 transverse bars of the same material as the sheath are formed. When the 

 sheath hardens, the transverse bars are destroyed by the pressure of the 

 growing cells. 



The Vegetative Cells. — The cells are arranged in a single row inside the 

 sheath, and are 1-1 in width, and, on the average, 4-6 in length. 

 The cell has a distinct membrane, inside which cytoplasm and reserve 

 matter, in the form of oil globules and glycogen, may be distinguished. 

 Small, clearer spaces in the cytoplasm may also be distinguished, but their 

 nature is regarded as doubtful, as they might either be vacuoles or empty 

 spaces left after the removal of the reserve material. 



Cell-division. — Is of the same nature as the same process in the orders 

 Bacteriacee and Coccacete ; a transverse wall is thrown across, being followed 

 by constriction at the same point ; the constriction extends until the two 

 daughter-cells are separated. Cell-division in the attached threads is more 

 active near the base than at the apex ) but, in the case of motile threads, is 



