146 INTERNATIONAL CONGRESS OP VITICULTURE 



The increase in the size of the stem is apparently not due to hyperplasia. 

 but rather to a slight hypertrophy of the cells, and to the intussusception of 

 a large amount of mycelium between the cells. (PI. V, figs. 1 and 2). The 

 water-soaked appearance of the diseased stems is in all probability the result 

 of an excessive amount of sap in the intercellular spaces. This phenomenon 

 may be caused by a change in permeability of the plasma membrane, possibly 

 induced by the presence of the fungus. 



As in the leaf the cells are ultimately killed and collapse, so producing 

 the brown sunken areas in the stem. 



In the livid berry the chlorophyll is acted upon as in the leaf and the 

 green color lost, thus giving the peculiar blanched appearance so character- 

 istic of this stage. In a short time the cells begin to collapse, the contents 

 become more or less plasmolysed and the walls brown, resulting in the well- 

 known soft, brown-rot stage. 



The color of the prematurely ripened grapes is located in the outer six 

 or seven layers of cells. It is due to the formation of some red substance in 

 the cell-sap. This may occur in the cells immediately adjacent to the 

 mycelium or several cells distant. It is very similar in appearance to the 

 changes occurring in the normally ripening grape. 



Pathological Physiology. 



The question of the resistance or immunity of certain varieties of grapes, 

 of different organs of the same variety, and of the same organ at different 

 ages and seasons has been seriously considered and investigated for some 

 time, particularly during the past five or six years. 



Bottini (1909) determined that when leaves of susceptible varieties were 

 immersed in or sprayed with the sap expressed from the leaves of a resistant 

 variety, the former were less easily infected than when water was used. It 

 is his opinion that the concentration of the sap of the resistant variety is the 

 controlling factor in this case. 



Laurent (1911.) obtained the concentration of the cell sap of different 

 parts of a vine and from different varieties. The method employed was to 

 determine the freezing-point of the expressed juice, the freezing tempeature, 

 according to Livingston (1903) varying inversely with the concentration or 

 the osmotic pressure. In this manner it was determined that the cell sap 

 of the older leaves is much more concentrated than that of the younger 

 leaves and that the sap of the berries is much less concentrated than either. 

 In every case the least resistant parts of varieties contained less concen- 

 trated sap. With this as a basis he formulates the theory that resistance is 

 the result of a more highly concentrated cell sap. He points out further that 

 Miintz has stated that resistance becomes greater as the water content falls 

 below 60 per cent. 



Cercelet (1912), Capus (1913), Larue (1912) and many other European 

 investigators are of the same opinion concerning the explanation of resist- 

 ance. Cercelet states that nitrogen, inducing a succulent growth raises the 

 water content and thus tends to render a vine more susceptible. On the other 

 hand, potash and phosphate are said to increase the concentration of the cell- 

 sap. Capus has made many interesting observations in this connection. He 

 claims that vines grown on a gravelly soil are in general more resistant than 

 those on a clay soil. In his opinion there are three stages of resistance in the 



