S. (I Paink 63 



mycological than by tlie bacteriological side of plant pathology. The 

 investigation of bacterial parasitism in plants above all things demands 

 of the plant pathologist an extremity of patience with which few perhaps 

 are gifted. The difhculties met with in the isolation of the parasite from 

 diseased plant tissues are infinitely greater than those encountered in the 

 isolation of an animal parasite. The animal pathologist has in the blood 

 a very specialised medium which excludes almost entirely the invasion 

 of saprophytic forms; on the contrary, the sap of the plant cells is 

 eminently suitable as a medium for the growth of many common 

 bacteria, and, situated as the plant is in a soil containing upwards of 

 five million organisms per gram, when once its defence against parasitism 

 has been broken down by the entry of a parasite, many of these common 

 soil organisms enter the diseased tissue and multiply luxuriantly often 

 to the partial, and sometimes even to the total, exclusion of the original 

 parasite. In attempts to isolate the parasite from potato stems affected 

 with "Blackleg" the author spent several months batthng with a 

 multitude of saprophytes before success attended his efforts, and then 

 only by chance was a colony of the parasite discovered on a plate con- 

 taining some 200 others of which thirty had been already investigated 

 and proved to be saprophytic organisms. In one investigation upon 

 which he is at present engaged more than 400 cultures have already been 

 made and many more will be necessary before the investigation is satis- 

 factorily concluded. Again Smith and Townsend(i4) worked most 

 patiently for three years upon the "Crown Gall" disease before the 

 causal organism was tracked to his lair. Another instance may be cited 

 in emphasis of the difficulties encountered in this branch of pathology; 

 Schiff-Giorgini(-ii) in investigating the Olive Knot disease worked for 

 two years upon an organism thought to be B. Oleae which was later 

 shown by Smith (43) to be a common soil organism and incapable of pro- 

 ducing the disease. To quote from Smith (45), "The labor involved is 

 enormous and exacting to discouragement at times, the results come so 

 slowly, so much must be done to be certain of so little, all because the 

 organisms dealt with are very small — hoiv small, we seldom realise ! " 



The British literature on bacterial diseases is so scattered and so 

 fragmentary that it seems advisable to collect together the fragments 

 and to "take stock" of our position. An attempt is therefore made in 

 this article to bring together the known facts about our bacterial diseases 

 in the hope that it may be useful to those engaged in diagnostic work, 

 and that it may in some measure stimulate the advancement of this 

 important branch of phytopathology. 



