92 MASS. EXPERIMENT STATION BULLETIN 175. 



on the effects of colored light on mosaic-diseased plants, and as a 

 result of his experiments stated that a cure was effected by blue light, 

 red light diminished the disease, and suffused light checked it somewhat. 

 In brief, his methods of experimentation and conclusion were as follows : — 



The diseased leaves of a plant were covered with a cloth hood of the 

 desired color, of a sufficient size to allow ample room for growth. The 

 apparently healthy basal leaves were left uncovered and exposed to the 

 normal daylight. After a time the hoods were removed, and it was found 

 that in the case of the plants exposed under the blue hood a cure was ef- 

 fected; those exposed under a red hood showed a duninution in the 

 severity of the disease; and in the case of plants exposed to the suffused 

 light alone the disease was somewhat checked. The cloth used for the 

 red and blue hoods was a rather coarse cotton material similar to that used 

 for making flags. 



Several investigators had noted the apparent beneficial effects resulting 

 from growing diseased plants in suffused light, but Lodewijks was the 

 first to really study the effects produced by colored light, although Bauer 

 appears to have made some observations on this point. As in no case 

 could the writer find that Lodewijks in his work had reinoculated from the 

 apparently cured plants to healthy ones, to prove the presence or absence 

 of the causal agent, and as it is often present and active in apparently 

 healthy leaves of diseased plants, as has been shown many times, it was 

 thought necessary to settle the point as to the presence or absence of the 

 causal agent in plants treated as in Lodewijks' work. 



Method. — The method of treatment of diseased plants was in every 

 way similar to that employed by Lodewijks as to texture of cloth, methods 

 of covering the plants, etc. The cloth covers were held away from the 

 plant by means of wire hoops, and the cloth was tied around the stem of 

 the plant below the diseased leaves. Plate V. shows a hood in place over 

 a field-grown plant, and gives a clear idea of the arrangement of the hoops, 

 etc. 



The cloth used was a coarse grade of cotton, and the colors were cad- 

 mium orange, ox-blood red and induHn blue. ^ 



Plants showing well-developed symptoms of the mosaic disease w^ere 

 selected for the experiment, none of which had less than four character- 

 istically diseased leaves, the lower remaining leaves apparently healthy. 

 The hoods were placed over the diseased leaves as above noted, and left 

 on for the required time, in most of the experiments twenty to thirty 

 days. At the end of this period the hoods were removed and the plants 

 carefully examined for visible symptoms of the disease. Two leaves from 

 the upper (i.e., the part under the hood) portion of the plant were removed 

 under absolutely aseptic conditions, the juice expressed and healthy 

 plants inoculated therewith by means of glass capillaries inserted just 

 below the terminal leaflets. Control inoculations with distilled water and 

 boiled juice were also made at the same time. The plants, after the 



> Ridgway, Robert: Color Standards and Color Nomenclature. Washington, D. C. (1912). 



