312 The Action of Gravity upon Bacterium Zopfii. 



regards coiling as the result of geotropism, and a second factor wliich 

 he terms rotating mutation. In our case the coils may be related to- 

 the resistance of the gelatine and the negative geotropism. But 

 spirillar forms are well known throughout the microphytes ; they are- 

 present in Cladothrix and many more lowly-organised forms, and are 

 found abundantly in fluid. Do, therefore, the spiral forms which we 

 have described as forming in the gelatine correspond to the free 

 spiral forms of the above examples ? If they do, and we have not 

 sufficient evidence to say they correspond, then the forces concerned 

 in their formation in the one case would be equally applicable to the 

 other. 



DESCRIPTION OF PLATES. 



PLATE 1. FIG. 10. Represents a vertical streak inoculation upon agar. The irre- 

 gular growth is characteristic. 



FlG. 12. This represents a culture -which was first grown in an atmo- 

 sphere of carbonic acid, and the only growth obtained was the thick 

 irregular streak seen along the centre of the tube. It was then trans- 

 ferred to oxygen, and a pinnate growth obtained, as in the figure. 

 FIG. 14. A typical symmetrical growth obtained by centrif ugalising the 



culture tube in the horizontal. 

 PLATE 2. FIG. 23. Skein, or Medusa-like growth, obtained upon agar. 



FIG. 28. Zooglea threads, showing the phenomenon of twisting. Gelatine 

 growth. 



