REPORT OF THE SOCIETY 13 



true immunity and resistance, we find ourselves involved in a maize of anato- 

 mical, phj'siological, bio-chemical and ecological evidence and theories which 

 have been offered, some to explain specific cases of resistance and other to 

 explain the problem in general. Before entering into a discussion of these it is 

 well to have clearly in our minds the fact brought out by Butlei' in his paper 

 on "Immunity and Disease in Plants" (1) that what we commonh' think of as 

 infection consists of two stages; the first being the entrance of the parasite into 

 the tissues of the plant, and the second the establishment of parasitic relation- 

 ship with the host. Some fungi, such as the rusts, enter many plants from 

 which they cannot obtain nourishment, and consequently perish because 

 they are not able to accomplish the second stage of infection. 



After considering these two stages of infection one realizes that inununity 

 and resistance may be due to morphological and anatomical characters of the 

 plant which prevent the first stage of infection, or entrance of the parasite 

 into the tissues; or to bio-chemical properties or anatomical characters of the 

 tissues of the host which prevent the second stage of infection or the establish- 

 ment of parasite relation ship with the tissues of the plant. 



Some students of this subject consider that immunity due to morphological 

 and anatomical characters preventing the first stage of infection is disease 

 escape, and confine the term immunity to those cases, due to lack of compta- 

 bility of the parasite with the tissues of the plant. 



Cases of immunity or resistance due to the anatomical characters of the 

 host preventing entrance to the parasite are comparatively numerous (3). 

 Coffee leaf disease usaully starts on the undersurface of the leaf as there are 

 few stomata on the upper surface. Young beat leaves are practically immune 

 to attacks bj" Cercospora beticola because their stomata are so small as to be 

 incapable of opening widely enough to allow for the entrance of the germ tube 

 of the spores of the fungus, which can only enter the host through the mature 

 stomata (4). Certain varieties of plums are resistant to brown rot caused by 

 Scletrotinia cinerea, beacause the stomata soon become plugged with masses 

 of small parenchymatous cells. The toughness of the skin, the firmness of the 

 flesh, and high fibre contents are also important characteristics which make 

 varieties of plums resistant to brown rot. It has been found that as ripening 

 progresses the texture of the resitant varieties remains firm, while that of the 

 susceptible becomes softer. The stomata of Kanred wheat, which is resitant 

 to certain strains of Puccinia graminis tritici, are said to be of such a nature 

 as to "shut out most of the fungi"(6). In a more recent paper by Allen it is 



1. et 2. Butler, Edwin John, Immunity and disease in Plants, Agr. Jour. India 1918, (Spec Indian Sci. Congr. 

 No. 1028, 1918. 



3. Butler, Edwin John, I.e. 



4. Pool Veniss Alorrel & McKay, Marion B. Jour. Agr. Res. 5, No 2, No 22, 1011-1038, 1916. 



5. Valleau, W. D. Jour. Agr. Res. 5, No. 9, 365-395. N. 29, 1915. 



6. Allen R. F. Jour. Agr. Res. 23:2. 131-132, 1923. 



