168 THE SOIL FLORA 



of the medium like B. mycoidcs or full of clear drop-like areas like 

 B. megatherium. 



"Physiology. The typical group number is the same as that for 

 B. mycoidcs, B. 121. 2323072, although considerable variation has 

 been observed, particularly in the production of acid from sugars 

 and from glycerin. In the earlier work, two subtypes were recog- 

 nized, basing the distinction upon the production of acid from 

 glycerin; but no such distinction is now recognized, because of the 

 inconsistent results obtained in regard to acid production. Dextrose 

 is always acidified by this organism; sucrose is generally acidified ; 

 glycerin less frequently, and lactose very seldom. A strain that 

 acidifies lactose has always been found to produce acid from all 

 three of the other compounds. The production of acid from lactose 

 may be a better basis for subdividing the type than acid-production 

 from glycerin. Out of 130 cultures studied, 19 acidified lactose; 

 but it seems unwise to consider them as constituting a separate 

 species, in view of the variation that has been found when cultures 

 have been retested. 



"Although many of the spore-formers are active ammonifiers in 

 solution and occur in soils in comparatively large numbers, yet 

 it is doubtful if they play any very important role in soil fertility. 



"Although of considerable importance, except for the nitrifiers and 

 some other organisms concerned with the transformation of nitrogen, 

 scant consideration has been given to any non-spore-forming bac- 

 teria found in soil." 



Ps. fluorescens which belongs to this group is described by Conn 

 as follows: 



"Ps. fluorescens (Flugge) Migula. The most striking character- 

 istic of this type is its fluorescence, which is observed in broth, 

 beef-extract-peptone agar, and sometimes in gelatin. Ability to 

 produce fluorescence is often lost, however, and then the type must 

 be recognized by other characteristics, such as rapid liquefaction 

 of gelatin, uniform turbidity in broth, cloudy, structureless colony 

 in gelatin, and acid production from dextrose. 



"Morphology. Hods 0.4 to 0.8 by 0.8 to 1.5 microns in old cultures 

 nearly the same shape and size as in young cultures. Flagella 3 to 

 6, arranged in a clump at one pole. Motility great. Rods do not 

 form chains. 



' ' Cultural Characteristics. G ood growth in broth ; no surface growth, 

 uniform turbidity, causing distinct cloudiness of medium; sediment 

 scant or none. Gelatin colonies liquefying with great rapidity; 

 round to irregular in shape, cloudy, structureless, occasionally 

 fluorescent. Growth on agar streak cultures, smooth, soft, glistening 

 generally causing the medium to show a green fluorescence. 



"Physiology. The typical group number is Ps. 211.2332133. 

 Fairly consistent results can be obtained in determining its group 



