74 SULPHUR BACTERIA 



siilfiiratiim, Beggiatoa roseo-persicina, and Thioporphyra volu- 

 tans ; and probabh^ of other sulphur bacteria not yet fully in- 

 vestigated. It has also been shown that the zoogloea condition 

 is frequently found in some of the sulphur bacteria ; that in 

 some species almost every shape known in the sulphur bacteria 

 may be found ; that in some cases the actual transition from 

 one form to another has been directly observed ; and that 

 two organisms, apparently specifically distinct, have been 

 observed in organic connection. Hence pleomorphism may 

 be a useful aid in the separation of species, if it can be shown 

 that in certain species its appearance is a regular occurrence. 



(6) Mode of Geyniination of the Spore. — The germination of 

 the spore in the genus Bacillus is not uniform in all species 

 of that genus. As, however, spore formation, with one or 

 two exceptions, is confined to that genus, this feature cannot 

 be used in the classification of the sulphur bacteria. 



ij) Method of Cell Division. — With greater knowledge it 

 may be possible to utilize the undoubted differences that exist 

 in the method of division of the cells. In the genus Bacillus 

 cell division is preceded by the formation of a plasma-derived 

 wall cutting across the cell. This wall then undergoes 

 longitudinal division, the process resembling in all essentials 

 the method of cell division which is followed in the higher 

 plants. On the other hand, in the genus Spirillum, the cell 

 contents withdraw from a certain area, separating the two 

 daughter cells which even at this stage are organically separated; 

 and are kept in place only by a connecting bridge of slime. 

 Complete separation follows the disappearance of the slime (see 

 Ellis (i)). lliis method occurs where a definite cell membrane 

 is not formed, and it is general among animal cells. With one 

 or two exceptions, e.g. Beggiatoa mirabilis, the cells of the 

 sulphur bacteria divide by the second method. This difference 

 in the mode of division could be used with advantage in the 

 classification of the sulphur bacteria were it not that the number 

 in which the first method prevails is so small that its use would 

 not have much value, and that there are too many organisms 

 among the sulphur bacteria of which the exact method of cell 

 division is unknown. 



