12 H. L. Russell. 



tissues of the stem and leaves. This result would have been much 

 more convincing had he used larger plants than wheat, as it is quite 

 possible that the bacteria isolated came from the surface rather than 

 the inner tissues of the plant. 



Although it is extremely doubtful if those micro-organisms 

 whose mode of nutrition is not adapted for parasitical existence in 

 vegetable tissues, can enter the plant without the intervention of 

 an actual wound, it is much more probable that those forms naturally 

 parasitic on plants may sometimes succeed in thus getting a foothold 

 in the tissues. 



Bolley, 1 in his work on surface scab of potatoes, tried the experi- 

 ment of infecting sound, healthy, growing tubers with liquid cultures 

 of the scab bacilli. The growing tubers, after thorough cleansing, 

 were immersed in a fluid containing an infusion of the scab bacilli, 

 and the glass vessel was then protected from outside contamination. 

 In thirteen days the tubers so treated had decayed, while a control test 

 with sterilized water showed tubers perfectly sound and the water 

 clear. He reasons from this that the bacteria penetrated the growing 

 lenticels of the tuber. He also repeated the experiment by saturating 

 with an infusion of scab bacilli sterilized soil in which he transplanted 

 the growing tubers. Control tests, watered with distilled water in- 

 stead of the diluted culture, were made, and he found that infection 

 took place when the bacteria came in contact with the healthy tuber. 



With the pear-blight germ I have found it impossible to infect even 

 the young budding leaves and stems of the pear, when these organs 

 were several times sprayed with a culture of the germ. Susceptible 

 as well as refractory varieties failed to succumb to the disease when 

 subjected to this manner of infection. Atomizing the flower clusters, 

 however, usually yields positive results, according to Waite. Here 

 the tissue is thinner walled, and in some places, as the nectary, is 

 destitute of cutin, so that the bacteria have less difficulty in effect- 

 ing an entrance. The highly nutritious nectar affords them an 

 excellent medium for growth, and here they are able to thrive until, 

 as Waite has suggested, they get a foothold. It is quite possible that 

 this intermediate stage of development affords an opportunity for 

 the accumulation of a ferment by which the germs are able to more 

 easily penetrate the subjacent tissue. 



1 Bolley : Agric. Science, Vol. IV, 250. 



