124 THE CYTOLOGY AND LIFE-HISTORY OF BACTERIA 



It is unfortunate that the cytology of this interesting process has never been 

 properly described. The vegetative cells are quite similar to those of eubacteria, 

 but the minute structure of the swarmcrs has never been described. 



Certain caulobacteria possess a short cycle which is rather similar. The 

 sessile, stalked bacterium produces a succession of motile, flagellated daughter 

 cells, which swim actively until they fmd a suitable attachment upon which 

 to form a stalk, and produce a new, sessile generation. 



There is no apparent difference between the daughter cell which, having 

 the terminal stalk, remains attached to the substrate, and that which, being 

 free, swims away, but the effect is exactly as though a sessile, asexual generation 

 were producing a series o( motile buds. If this type of organism possesses a 

 sexual stage, it is in the motile cells that it must be sought. 



F: GONIDIA AS A STAGE IN THE BACTERTiL 

 LIFE-CYCLE 



(i, 6, 7, 17, iX, 22, 36, 40, 42, 43) 



This question, so far as it relates to the tubercle bacillus, has already been 

 discussed (Chapter V). Of the many claims that bacteria of other groups 

 may reproduce by the liberation of tiny, fdterable granules or gonidia, few 

 have been accompanied by sufficiently detailed, cytological information. 



By far the most perfect examples of gonidial reproduction are provided 

 by the nitrogen-fixing bacteria Azotohactcr and Rhizohium. The details in 

 both cases have long been known, but have been described in a rather un- 

 convincing manner, and, in the case of Rhizohium, not entirely accurately. 

 It was supposed that large " barred " bacilli fragmented to form small 

 coccoid swarmers ; each dark bar representing the genesis of a single swarmer. 

 In fact, the process is alike in both genera. The tiny, polar-flagellated gonidia 

 form within the lumen of large mother cells, and are released by rupture of 

 the cell wall. The mother cells in the case of Rhizohium are divided by 

 basophilic septa, probably secretory in function, and these septa are the " bars " 

 of the earlier account. 



A second, larger type of gonidium, resembling a small vegetative cell, 

 may be produced by Azotohactcr. 



