CHAPTER IV 



VARIATIONS IN MORPHOLO&T 



Variations in morphology will be considered under three 

 heads: (A) zoogleic forms, (B) individual organisms, (C) 

 colonies. 



A. Zoogleic Forms. 



One remarkable feature of the bacteria or schizomycetes 

 is the tendency they show when multiplying to become massed 

 together, not indiscriminately but in an orderly arrangement, 

 to form "zoogleae." These forms display an extraordinary 

 diversity of shape and structure. Thus, a single bacillus — as 

 a result of alternate elongation and division in a transverse 

 plane — may give rise to a long filament consisting of a row of 

 cylindrical cells placed end to end. In other cases a number 

 of organisms may be crowded together in. a round gelatinous 

 mass, their swollen cell walls fusing to form a mucilaginous 

 matrix in which they lie embedded for an indefinite period. 



The shape and structure of these zoogleae are not fortui- 

 tous but appear to be designed in many instances to attain 

 some definite object of advantage to the organism, and may 

 thus form a stage in its life history. This is the case for 

 example in the Bacterium radidcola, the nitrogen-fixing 

 organism found in the nodules on the roots of leguminous 

 plants. It first enters the root hair from the soil; it then 

 assumes a filamentous form and — in a manner comparable to 

 the downward growth of the pollen tube from the stigma to 

 the ovary — pushes its way along the interior of the hair as 

 a long slimy thread until it penetrates the tissues of the root 

 itself. 



Again the Beggiatoa versatilis, a vegetation often seen at 

 the mouth of drain pipes, may be observed to send out from 

 a whitish gelatinous ground mass, long oscillating filaments 



