Apkil 14, 1916] 



SCIENCE 



537 



at the British Medical Association were veri- 

 table triumplis. 



His final seventeen years at the 'New York 

 Public Library were the culmination of his 

 laborious and distinguished life. 



Samuel D. Gross, Weir Mitchell and Bill- 

 ings were by all odds the most widely known 

 American medical men in the last half of the 

 nineteenth century. 



Dr. Garrison's book is delightful. He is 

 judicious in his selection from Billings's 

 Letter and Addresses. His style and his gen- 

 eral review of the various stages of Billings's 

 development and of his character and per- 

 sonality leave nothing to be desired. The only 

 regret I have is that he takes as I think a 

 backward step in using the archaic and 

 souperfluous " u " in labour, endeavour and 

 their similars. 



W. W. Keen 



SPECIAL ARTICLES 



EFFECT OF COLORED LIGHT ON THE MOSAIC 

 DISEASE OF TOBACCO 



In connection with extended work on the 

 mosaic disease of tobacco in this section of 

 the Connecticut Valley, it was found that 

 plants grown imder shade or tents appeared to 

 be much less affected with the mosaic disease 

 than those grown in the open. This fact had 

 previously been noted by Sturgis'^ in Connec- 

 ticut, and the writer, in conjunction with 

 other work on this disease, outlined experi- 

 ments relative to a study of light conditions 

 on the intensification or reduction of the dis- 

 ease. 



While the writer's preliminary work was in 

 progress, his attention was called to a paper 

 by Lodewijks^ published in 1910, which dealt 

 with the effects of colored light on mosaic dis- 

 eased plants. As a result of his experiments 

 Lodewijks stated that a cure was effected by 

 blue light; red light diminished the disease, 



1 Sturgis, W. C, "On the Effects on Tobacco 

 of Shading and the Application of Lime, ' ' Conn. 

 Agr. Exp. Sta. Ann. Kept. 23: 252-61, 1899. 



2 Lodewijks, J. A., Jr., Zut Mosaikkrankheit des 

 Tabaks. Kee. Trav. Neerlandais, Vol. 7, 107-29, 

 1910. 



and suffused light checked it somewhat. This 

 is not the place for an extended discussion of 

 his methods of experimentation, but in brief 

 it may be stated that the diseased leaves of 

 the plant were enclosed in a cloth hood of the 

 desired color, the apparently healthy basal 

 leaves remaining uncovered and exposed to 

 normal daylight. After some time the hoods 

 were removed and the plants examined for 

 symptoms of the mosaic disease. The results 

 obtained, if substantiated, would be of great 

 interest and value. In order to satisfy himself 

 the writer duplicated in so far as was possible 

 the work of Lodewijks, employing the same 

 methods and cloth hoods of approximately the 

 same texture as those used by him in his ex- 

 periments. The hoods were allowed to re- 

 main over the plants for thirty days; at the 

 end of this period they were removed and the 

 plants carefully examined for visible symp- 

 toms of the disease. The results obtained 

 were in brief as follows: 



The plants covered with the red cloth hoods 

 showed a diminished color variation between 

 the light and dark green areas of the diseased 

 leaves, and all new growth showed a more or 

 less pronounced mottling. After remaining a 

 week exposed to normal daylight, all the new 

 growth was badly diseased. Healthy plants 

 inoculated with juice from the treated leaves 

 became diseased in from ten days to two 

 weeks. Control inoculation remained healthy. 

 From the above results it may be stated that 

 there is a diminution in color variation in 

 diseased leaves, not of a permanent character, 

 however, and the active principle of the dis- 

 ease remains very virile and highly infectious. 



Similar experiments carried on with blue 

 cloth hoods gave the following results: On 

 three plants after thirty days' treatment no 

 visible symptoms of the mosaic disease were 

 observable, although there was a slight tend- 

 ency towards curling noticeable on a few 

 leaves of the new growth. One other plant, 

 however, showed a slight mottling on two of 

 the young leaves. Two weeks after the hoods 

 were removed, the first three plants did not 

 show any marked symptoms of the mosaic 

 disease other than a faint mottling of a few 



