14 FIELD STUDIES OF THE CROWN-GALL OF THE GRAPE. 



DEVELOPMENT OF THE DISEASE ON SEEDLINGS. 



The seedlings used in the experiments described in this bulletin, 

 unless otherwise designated, were grown from seed sterilized in con- 

 centrated sulphuric acid for ten minutes, neutralized with a 10 per 

 cent water solution of potassium hydroxid, and then washed in sterile 

 water. These were planted and grown in soil sterilized in an auto- 

 clave at a temperature of 110° C. (230° F.), placed either in pots 

 similarly sterilized or in benches constructed of new pine and cypress 

 lumber, and washed on the surface with a 2 per cent water solution 

 of copper sulphate. 



Seedlings of the following varieties of grapes were grown under 

 these conditions: Flame Tokay, Muscat of Alexandria, Mission, 

 Malaga, Black Malvoisie, Concord, Delaware, Catawba, and Niagara. 

 All such seedlings remained free from the disease except where they 

 were wounded and inoculated either with pieces of root galls or with 

 cultures of bacteria. The galls on small seedlings develop at a much 

 more rapid rate than the diameter of the canes or roots of the plants on 

 which they occur; for example, on the root of a vine with a diameter 

 of a quarter of an inch a gall developed in two months with a diameter 

 of an inch (PI. Ill, fig. 2). 



Cane galls did not develop on any of the plants in the experiments, 

 as all inoculations were made on the vines either at or just below the 

 surface of the soil. 



DEVELOPMENT OF THE DISEASE IN VINEYARDS. 



In vineyards wherever the disease is found in its worst forms the 

 galls are developed on the roots in great numbers by the end of the 

 third year from the time of planting the vines. Beginning about the 

 fourth year there takes place a development of galls on the canes of 

 some of the diseased plants, but on many vines the disease develops 

 only below the surface of the soil. 



THE EFFECT OF CROWN-GALL. 



The presence of the disease on grapevines becomes apparent 

 within a short time after they are attacked. Usually the leaves lose 

 their healthy dark-green color and become more or less chlorotic, 

 varying with the intensity of the disease. The growth of the canes 

 becomes slower until they die above the point of attack, due to the 

 cancerous effect of the disease. 



The galls have a poor epidermal covering, which is constantly being 

 ruptured during their development. This permits the evaporation 

 of the sap of the vines. In the dry climate of the southwestern United 

 States this loss of sap easily becomes a serious matter and quickly 

 results in the lowering of the vitality of the diseased vines. 



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