274 



STRUCTURAL BOTANY 



understood. So far as we know at present, however, the 

 structure appears to be very simple. There is a definite 

 membrane which, however, does not consist of cellulose, 

 but seems to be chiefly of a proteid nature. The cells 

 move actively, and their movements are now known to 

 be due to cilia which are attached to the membrane, a 

 proof in itself that the latter must be of a very different 

 character from the cell -wall of 

 ordinary plants (see Fig. 109, B). 

 The whole interior of the cell 

 is usually occupied by the proto- 

 plasm. It has not been proved as yet 

 that a nucleus is present, though at 

 certain stages rod-like bodies have 

 been detected in the cells, which 

 may turn out to be of that nature. 

 For some time the Bacillus 

 FIG. 109. Bacillus subtilis. continues in the actively swarm- 



A, cells cohering in fila- . . J 



merits ; the dark bodies ing condition, multiplying abund- 

 antly by the repeated transverse 

 division of the cells. After some 



are spores. B, swarming 

 ciliated cells produced on 

 germination of the spores. 

 Magnified 800. 

 Strasburger. ) 



(After ^yg fo Q i n divid ua i s begin to seek 

 the surface of the liquid, where 

 they pass into a resting condition. At this stage the 

 cells remain connected together in long filaments, and 

 their outer cell-walls become very gelatinous. This is 

 called the zoogloea condition, and is easily recognised 

 by the gelatinous iridescent film which the colonies of 

 the organism form on the surface. 



Lastly, when the food in the liquid is getting ex- 

 hausted, the spores begin to form. This takes place 

 after locomotion has ceased and the Bacillus has entered 

 the filamentous condition (see Fig. 109, A). The spores 



