264 A Case of Recovery from Mosaic Disease of Tomato 



In 1910 Lodewijks 1 published the results of his investigations on 

 mosaic disease. He covered the upper diseased portions of mosaic 

 plants and at the same time exposed the lower apparently healthy 

 leaves to light of different colours. Under these conditions he found 

 that diffused light checked the disease, red light decreased it, and blue 

 light completely cured plants of the malady. These very striking 

 results still await confirmation. 



Allard writing in 1914 2 states that "Some practical growers have 

 claimed that the disease can be checked if taken at its first appearance 

 by pulling affected plants until they are loosened from the soil." Of 

 this he remarks " There is little in this view however to recommend its 

 general adoption" and that "In the writer's experimental tests many 

 thousands of affected plants have been kept under observation through 

 all phases of the disease. In no instance has there been a case of actual 

 recovery from true mosaic disease." 



Allard's experience confirms that of practically all recent investi- 

 gators of this malady. 



Thus Clinton 3 writes : " A plant which once becomes infected remains 

 so, and all subsequent new growth (at least that above the lowest 

 infected leaf) usually, if not always, becomes calicoed." "The clause 

 is placed in parentheses because we are not sure whether the calico 

 virus is carried downward in the stem as far as, or as readily as it is 

 carried upward. If not, it stands to reason that if plants were calicoed 

 late in life by touching and infecting the upper leaves only, and some 

 time later were cut off at the base with a sterile knife the resulting 

 suckers would not so surely calico as those from plants whose basal 

 leaves were calicoed. Some evidence along this line is shown by 

 experiment No. 124, where the juice from an apparently healthy leaf 

 at the base of a plant calicoed above, failed to infect another plant 

 when applied to it." 



Chapman 4 , writing in 1913, states: "Once the disease appears on 

 a plant, all subsequent growth will be mosaic to a greater or less extent." 



Moreover any apparent cases of recovery in the past are rendered 

 extremely improbable in view of the fact recently demonstrated by 

 Allard 5 that the virus of the disease may be present in a highly infective 

 condition, and yet produce no external symptoms. This fact, that an 

 individual may be diseased and serve as a centre of infection, whilst 



1 Bee. Trav. Neerland. vn. (1910). 



2 U.S. Dept. Agr. Bull. 40 (1914). 3 loc. cit. (1914). 

 4 Ann. Bept. Mass. Agr. Expt. 8ta. 1't. xi. No. 31 (1913). 8 loc. cit, 



