S. G. Paine 73 



of fungal origin until 1912 when Cunningham (ii) showed the relation of 

 Oospora scabies to the bacteria. In 1914 this organism was referred by 

 Lutman and Cunningham (20) to Actinomyces chromogenus a species 

 previously described by Gasperini(M). 



Lutman and Cunningham have obtained four strains of Actinomyces 

 chromogenus Gasperini from scabbed potatoes in America. Whether the 

 cause of the disease is the same in this country is still uncertain, and 

 the investigation of this matter is one of the many problems iii plant 

 bacteriology which call for elucidation. It is very unsatisfactory that 

 a disease so long-established in the country should not yet have been 

 attributed to a definite organism. 



Crown Gall. 



An intumescence disease on the roots of various plants has been fully 

 described by Smith and Townsend(44). The same symptoms of disease 

 have been found on the roots of Paris daisy (25) {Chrysanthemum frutescens 

 L.) grown at Kew; although the organism has not been isolated here 

 there seems little reason to doubt that the disease is etiologically identical 

 with that in America. 



A very large number of host plants have been found to be affected 

 with this disease. In this country they have been observed also in plum, 

 rose, raspberry and loganberry and in the United States on peach, 

 apricot, almond, prune, apple, cherry, poplar, chestnut and blackberry. 



So-called Physiological Diseases. 



A number of obscure diseases have been attributed to a derangement 

 of the normal physiological condition of the plant without the inter- 

 vention of a parasite. This is in all probability a lame way of hiding our 

 ignorance, and the possibility of the existence of ultra-microscopic 

 organisms in these cases should »always be kept in the fore-front. 



The "Leaf-roil" disease of potatoes has been investigated thoroughly 

 by Quanjer(40) who finds a pathological condition of the phloem elements 

 of the stem to which he ascribes the visible symptoms of disease. The 

 facts that the disease is communicable to a scion by grafting a disease- 

 bearing stock and vice versa and that it is transmissible through the soil 

 would seem to point strongly to a bacterial origin of the disease, and 

 further investigation is advisable before any cause other than a parasitic 

 one is accepted for this disease. 



