310 Prof. R. Boyce and Mr. A. E. Evans. 



in the case of gravity. The angle remains about the same, and on 

 microscopic examination the rami are found in nearly all cases strictly 

 parallel and unbranched. 



Our experiments thus show that we get a pinnate growth o 

 'Bacterium Zopfii when the surface of the medium is kept in or near 

 the vertical, or when the culture is rapidly rotated in the horizontal. 

 That an irregular growth obtains when the gelatine surface is hori- 

 zontal, or when it is slowly rotated in the vertical. That it is 

 necessary in order to demonstrate the upward growth to have a 

 suitable temperature and suitable medium, and that other factors, 

 the nature of which we do not understand, probably likewise influence 

 the symmetrical growth. We would also draw attention to the fact 

 that on vertical or nearly vertical gelatine surfaces, an irregular 

 growth usually spreads downwards (compare fig. 6) upon the 

 surface, and that when a horizontal surface of gelatine is inoculated, 

 extension of the organism takes place vertically downwards into the 

 substance of the gelatine; but in neither of these cases are the 

 well-defined rami present. The question now remains, is the force 

 which induces the upward growth of the protoplasmic threads of 

 Bacterium Zopfii, gravity ? Rozanoff* brought forward a beautiful 

 example of upward growth in one of the Myxomycetes, JEthalium 

 septicum. He grew it upon a nearly vertical surface of filter paper 

 through which a very slow stream of water must have been con- 

 stantly passing, as the upper edge of the paper rested in water. He 

 found that the fungus grew upwards. He repeated Knight's centri- 

 fugal experiment, and found the fungus centripetal ; during this- 

 experiment the filter paper was kept moist with water, and therefore 

 the latter must have tended to fly outwards. He grew the jEthalium 

 upon a horizontal surface of paper, across which a slow stream passed 

 from one side to the other, and he found that growth did not take 

 place more against the stream than with the stream. He argued 

 whether this w r as an example of negative geotropism or of growth 

 induced by the contrary stream of water, and he concluded that 

 JEthalium was negatively geotropic, but that the contrary flow of 

 water acted like the force of gravity and of centrifugalism. To our 

 minds this does not seem an illogical conclusion, but Strasburger 

 maintained that it was an example of rJieotropism alone. Rheotrop- 

 ism, as far as fluid is concerned, cannot enter into our case. Ouy 

 tubes were always plugged with absorbent cotton wool, and were not 

 capped, and we never noticed moisture upon the surface of the gela- 

 tine, and, in any case, the geotropic rami tend to very slightly or 

 deeply penetrate the gelatine. We have stated that both in vertical 

 and centrifugal ised gelatine growths, rami tend to pass deeply into- 

 the gelatine. Now we have observed, when we have placed in the 

 * ' Mem. Soc. Imp. des Sciences, Cherbourg,' vol. 14. 



