Section C— BOTANY. BACTERIOLOGY. AGRICULTURE, 

 AND FORESTRY. 



Prksident of the Section : — Ethel W. Doidge, M.A., D.Sc, 



F.L.S. 



MONDAY, JULY 7. 



The President delivered the following^ address : — 



THE ROLE OF BACTERL/V IN PLANT DISEASES. 



The discovery of the causal relation of bacteria to plant 

 diseases is the greatest contribution to phytopathology since the 

 classical work of de Bary on the parasitism of the fun^i. If we 

 except the discovery of bacteria in the root nodules of the 

 Le.ejuminosae, by Woronine (68) as early as 1866, the earliest 

 work on the relation of bacteria to plant diseases was that 

 of Burrill, an American phytopathologist. who, in 1878 ( lo-ii) 

 showed that the disease known as pear blig^ht, which had for many 

 years caused serious losses in the United States, was due to the 

 attacks of a micro-organism which he named Micrococcus 

 amxJovorus. This was followed in i87q by Prillieux's papers on 

 a pink discolouration of wheat, due to a Micrococcus (41. 42), and 

 by Wakker's work on the yellow disease of hyacinths, published 

 between the years 1883 and i88g (64-65). 



In spite of the evidence brouo^ht forward by these and other 

 workers, great reluctance was still shown bv manv eminent 

 botanists to admit the truth of their conclusions. Hartig (25) 

 expressed the opinion that, owing to its peculiar structure and 

 the absence of circulatory channels which would serve for the 

 distribution of micro-organisms, the plant is protected from 

 their attacks ; and that the cell sap. being acid in reaction, is an 

 unfavourable medium for their growth. In 1882 Hartig gave it 

 as his opinion that there was no such thing as a disease of plants 

 due to bacteria ; in 1884 de Bary stated that they had scarcely 

 ever been observed, and in 1885 in his " Lectures on Bacteria, " 

 said that the present state of knowledge justified him in regarding 

 " parasitic bacteria as of but little importance as the contagia 

 of plant diseases." 



In spite of the opinions expressed bv these eminent path- 

 ologists, a mass of evidence in favour of the parasitism of plants 

 by bacteria gradually accumulated. Burrill's work on the pear 

 blight was confirmed bv Arthur (3, 4) (1884-6), and was fully 

 substantiated ten years later by Waite (62-63), who i.solated the 

 organism. Bacillus ■amylovonts, and was successful in reproducing 

 the disease by inoculation with pure cultures. Savastano (46) 

 demonstrated the constant occurrence of bacteria in the olive 

 tubercles, isolated an organism, and obtained typical knots on 

 healthy shoots by inserting minute quantities of the culture into 

 punctures. 



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