MOSAIC DISEASE OF TOBACCO. 



93 



removal of the leaves above mentioned, were allowed to grow to matm-ity 

 under normal light conditions. 



Most of the experiments were carried on in the greenhouse, where tem- 

 perature and other conditions were under more direct control than in the 

 field, although field experiments later repeated gave the same results, but, 

 of course, in this case there was a greater chance of subsequent infection 

 through careless handling, insect attacks, etc. In the following paragraphs 

 are tabulated the results of a typical series of experiments relative to the 

 effects of light on mosaicked plants. 



Experimental Data. 



Red Cloth. — Three plants were covered with the red cloth hoods for 

 twenty days. The covers were then removed, and in all cases visible 

 symptoms of the disease were still present, although the color variation 

 between light and dark green areas was not so marked as at the beginning 

 of the experiment. All the new growth, in addition to the leaves diseased 

 at the time the hoods were put on, also showed the mottling distinctly. 

 A week after the hoods were removed all the plants still showed the 

 disease in undiminished severity. 



Healthy plants inoculated with the juice from the leaves confined under 

 the hood became diseased in from nine to eighteen days' time. Controls 

 inoculated in the same manner with boiled juice from the same leaves, 

 and with distilled sterile water, remained with very few exceptions 

 healthy. Table IV. gives the results of the inoculation experiments in 

 one series. 



Table IV. 



Result of Inoculation with Juice from Plants grown under 

 Red Hoods. 



Controls inoculated with boiled juice, 10; diseased in eighteen days, 1. 



Controls inoculated with distilled, sterile water, 10; diseased in eighteen days, 0. 



From the above results it may be seen that there was a diminution in 

 the color variation in diseased leaves;, it was not of a permanent character, 

 the plants all showing the disease in undiminished severity again after a 

 short exposure to normal dayhght. The causal agent of the disease was 

 still highly infectious. 



