4 H. L. Russell. 



but few germs, we may safely conclude that they have either been 

 killed off by the plant or died from insufficient nutrition. 



On the other hand, an increase can only be considered probable 

 where the cultures, not only from tne tissue immediately surrounding 

 the inoculation point, but at a distance from it, reveal a large number 

 of germs. Even the fact that bacteria are to be found at a greater or 

 less distance from point of introduction does not necessarily show 

 that an actual increase has taken place. Their presence at this point 

 might be considered as due either to simple diffusion or to mechani- 

 cal transportation by the fluids of the plant. The effect of these 

 possible factors will, however, be shown later to be quite nugatory. 



If macroscopical changes are to be seen in the tissue, it would be 

 of itself sufficient evidence that actual multiplication of the micro- 

 organisms had taken place. In addition to culture methods to deter- 

 mine the presence or absence of bacteria in the infected tissues, sec- 

 tions were also subjected to microscopical examination. 



But this method proved quite unsatisfactory, except where the 

 bacteria in the tissues were numerous, as in the case of actual infec- 

 tion. The granular detritus and peculiar rod-like masses of proto- 

 plasm often found in matured cells make it extremely difficult to 

 differentiate the bacteria in an unstained condition. The use of 

 staining methods, so successful in the differentiation of bacteria in 

 sections of animal tissue, have not as yet been successfully applied to 

 bacteria in plants. The aniline stains, toward which the bacteria 

 are so susceptible, seem to impregnate the vegetable cell and its 

 membranes with great ease, and in the use of decolorizing agents, 

 parts of the plant cell retain the stain as deeply as do the bacteria. 



Before detailing the results of the experiments made, we will con- 

 sider briefly the presence of bacteria in normal uninjured plant- 

 tissues. This, for a considerable time, has been a debatable question, 

 and the recorded results of numerous observers are somewhat at 

 variance with one another. 1 The preponderance of evidence is, how- 

 ever, certainly against the view that micro-organisms are present 

 normally in the tissues of higher plants, and this conclusion harmon- 

 izes well with what we know in the domain of animal life. 



In the examination of plant-tissues I have made a large number 

 of cultures, according to the method described above, from plants 



1 See bibliography, page 34. 



