94 



MASS. EXPERIMENT STATION BULLETIN 175. 



In a second series the hoods were allowed to remain over the plants 

 for tliirty days, as it was thought that a twenty-day exposure might 

 have been too short, but no appreciable variation in the results was 

 obtained as a result of the longer treatment. 



Orange Cloth. — In this series two plants were covered with orange 

 hoods for a period of thirty days. On removing the covers it was found 

 that the visible symptoms of the disease were, if anything, intensified. 

 The gro"\\i:,h was somewhat more spindling, the leaves narrower, and the 

 light and dark green areas very clearly defined. Infection was produced 

 from both plants by inoculation into healthy plants. The causal agent 

 was very active and highly infectious. 



Blue Cloth. — The diseased parts of three plants were covered with blue 

 cloth hoods, as in the preceding experiments, for a period of twenty-five 

 days. The covers were then removed and a careful examination of the 

 leaves made. On plants A-2 and B-2 no visible symptoms of the mosaic 

 disease could be observed, although a slight tendency towards curling was 

 noticeable on a few of the leaves. The leaves were all uniformly light 

 green in color, and aside from this, appeared normal. Plant C-2, however, 

 showed on two leaves a slight mottling. Two weeks after the hoods were 

 removed, plants A-2 and B-2 did not show any marked symptoms of the 

 mosaic disease other than a faint mottling of a few leaves, not sufficient, 

 however, to seriously injure the leaf. Plant C-2 developed mosaic 

 again in the same length of time, but not as seriously as before the 

 treatment. It may be that the mottling on A-2 and B-2 was due to 

 the maturing of the plant, although this mottling is usually distinctive 

 enough to be readily differentiated from that caused by the mosaic 

 disease. 



Healthy plants inoculated with the juice of leaves from plants A-2, 

 B-2 and C-2 contracted the disease almost without exception. Controls 

 inoculated with boiled juice failed to develop the disease. Table V gives 

 the results of the inoculations. 



Table V. 



Results of Inoculations with Juice from Plants grown under 

 Blue Hoods. 



Controls inoculated with boiled juice, 6; diseased in eighteen days, 0. 

 Controls inoculated with sterile distilled water, 6; diseased in eighteen days. 



