424 SCIENCE PROGRESS 



too, the crushed tissue is somewhat more infectious than 

 the extracted juice, but aphids are the most consistently suc- 

 cessful agency for inoculation. In this case the virus is 

 present in the stem, leaves, flowers, and fruit, but is apparently 

 absent from the roots and usually from the seed. The leaf 

 hairs contain the virus, and it can be successfully inoculated 

 through broken hairs, just as in tobacco. Infection through 

 the roots and blossoms has not succeeded. Seedling plants are 

 less readily inoculated than those that are older but still growing 

 rapidly. After growth has reached its maximum inoculation 

 is again less often successful. The virus travels fairly rapidly 

 through the plant. In one case in an inoculation at the tip of 

 the stem, the juice of a leaf at the tip was infective twelve hours 

 sooner than that of a leaf at the base of the plant ; and in 

 another case it took only about nine hours to traverse thirty 

 inches of stem in an upward direction. Not only are practically 

 all the species of Cucurbitacese tested susceptible to this disease, 

 but it can be transmitted to members of several other families, 

 including Solanaceae, Compositae, Campanulaceae {Lobelia), and 

 Asclepiadacese. Besides aphids it can be transmitted by beetles 

 of the genus Diabrotica. 



In the mosaic disease of sugar-cane, maize, sorghum, and 

 various other grasses,^ juice inoculations by injecting a con- 

 siderable quantity of juice into the growing point have given 

 some successes, but far less than when insects were used. The 

 virus extends through the plant very slowly and healthy cuttings 

 may be obtained from the lower part of the sugar-cane for an 

 appreciable time after the top shows symptoms of the disease.* 

 Both in maize and sugar-cane, new suckers may come up from 

 diseased plants without showing any symptoms. There is also 

 some evidence in the mosaic disease of potato that the virus 

 reaches the tubers rather late in their development, and that it 

 is at least sometimes possible to harvest immature tubers from 

 diseased plants that may be used for " seed " without trans- 

 mitting the disease. 



The failure in most of the virus diseases of plants of trans- 

 mission by the seed is chiefly of interest as indicating that, 

 whatever the nature of the virus may be, it does not diffuse as 

 readily from the supports of the ovule to the embryo as the 

 organic nutrient materials do. In the quercina disease of 

 Datura transmission by the pollen occurs as well as by the female 

 gametes, and this appears to be the only case of the sort recorded. 



^ Brandes, E. W., The Mosaic Disease of Sugar-cane and other Grasses, 

 U.S. Dept. of Agric. Bull., 829, 1919, and Mosaic Disease of Corn, Journ. of 

 Agric. Res., p. 519, 1920. 



2 Lyon, H. L., Three Major Cane Diseases, etc., Bull. Exper. Stat. 

 Hawaiian Sugar Plant. Assoc, iii, p. i, 1921. 



