12 



BACTERIA IN RELATION TO PLANT DISEASES. 



tissues, it is sometimes desirable to grow tliem for a clay in bouillon before attempt- 

 ing the plate-cultures ; but one must then be on his guard, since it is quite possible 

 by this method to start with enormous numbers of the right organism and have the 

 bouillon culture filled with something else at the end of the 24 hours. 



Pure cultures may also sometimes be obtained l)>- cutting out pieces of the 

 tissue and throwing them into tubes of culture media. This method, however, 

 shoAvs little or nothing as to the prevalence of the organism in the tissues, and in 









_ it*. 



fS 



Fk- 7 



the hands of beginners is ver)' liable to miscarr\'. If growth is obtained it niav 

 indeed have come from many organisms of one sort pervading the tissues and 

 causing the disease, but it is not certain that it did not result entireh- from one or 



*Fio. 7. — Bundle in a cauliflower-petiole entirely debtroj-ed by Baclcrium cainpcslir. The re- 

 sult of a pure^culture inoculation. Plant No. 112 inoculated March 10, 1897, hy needle-punctures on 

 the blade of a leaf 'witbout hypodermic injection. First signs of disease Marcb 20. Petiole put into 

 alcohol on April 5. Longitu'dinal section. Tissues surrounding the bundle entirely free from bac- 

 teria. Section not made from the inoculated leaf, but from tlhe first leaf that showed secondary 

 signs. Drawn from photomicrograph of a paraffin section stained ivvith carbol-fuchsin. X 206. 



