19 



n. » 



n.2 



n.3 



• = Drop 



Diagram I. Showing the effects of different kinds of treatment on soil inoculated with 

 theDrop. n. i,n. 2, and n. 3, normal or untreated plots, a, covered with 3 in. of sterilized 

 soil, b, 3 in. of sterilized sand, c, J in. of sand. The dotted lines indicate the three inoc- 

 ulated rows of lettuce. 



quently pricked out when about one inch in height into larger boxes 

 of sterilized soil. \\'hen the plants had obtained half a dozen 

 leaves from 4 to 6 inches long, which is the usual size for the second 

 transplanting, they were put into the plots. By this precaution we 

 were tolerably certain that the plants were entirely free from Drop 

 when set out in the experimental plots and any infection which 

 occurred would of course be traced to the soil in the plots. By this 

 means we were able to observe the spread of the disease. Each 

 infected plant, when presenting its specific symptoms, was carefully 

 recorded together with data concerning its occurrence. The first 

 experiment relating to the Drop, which is graphically shown and suf- 

 ficiently explained for most purposes in Diagram i, gives us an idea 

 of the relative value of certain methods of controlling this disease 

 and also some idea of its rapidity of spreading. The three upper 

 rows in this experiment represented by the dotted lines were inocu- 

 lated with Drop infected soil as previously described, and the largest 

 number of infected plants are shown in the three back rows in which 

 the infection was placed. The encroachment of the Drop upon the 

 uninfected areas is well shown, although it is possible that some of 

 the other plants were infected in this experiment before being trans- 

 planted, as the soil was not in this instance sterilized, and we subse- 

 quently ascertained that the soil in which the young plants were 

 grown was not wholly free from Drop. Only one plant showed the 

 Drop when 3 in. of sterilized soil was placed upon the surface 



