THOMAS: INFECTION OF APIUM GRAVEOLENS 11 
to modify these conditions in celery plants by various methods of 
feeding and handling to determine the influence of such treatment 
upon the interaction of host and parasite. The direct effect upon 
the plants has been visible in some cases in the increase or decrease 
in growth, the putting out of new leaves or the dropping of old 
leaves and in the turgidity of the tissues. In other instances the 
reaction to the treatment was not so directly evidenced. The 
difficulty in obtaining properly controlled results is obvious, but 
I have made a number of experiments to test the amount and 
character of the infection produced by inoculating plants in 
different conditions of health more or less artificially induced. 
One of the first striking results noted was that which was 
produced by treating pot bound plants with sodium nitrate in 
solution. Five plants in four-inch pots of garden soil received 
each 1 gram of sodium nitrate in 100 c.c. of water. In this and 
in the succeeding experiments, the control plants received an 
amount of water equivalent to that used in the solution with the 
nutrient. The plants were inoculated at the time the nitrate 
solution was added. 
TABLE II 
INCREASE IN INFECTION PRODUCED BY TREATING POT BOUND PLANTS WITH SODIUM 
° 
NITRATE SOLUTION 
ire ive | Average No. 
are ON eS 7 Mester | ia 
| 
Sodium nitrate......... / 348 85 177 189 238 10.6. |>° 24.3 
Control. 2 ye ee | 234 fe) II 43 38 S°- Fo 10.0 
TABLE II shows the very marked increase in infection obtained 
upon the plants which received the fertilizer. This difference is 
unusually marked due to the fact that the plants were badly pot 
bound and growth had been markedly checked. 
With the garden soil used, the addition of calcium sulfate 
in the dry form, as it has been used in agricultural practice, pro- 
duced a small decrease in infection. This series was prepared by 
mixing about five grams of calcium sulfate with the soil of each 
pot at the time of repotting. Twenty-four days later these plants 
were inoculated with controls. After the records were taken 
these plants were kept upon the greenhouse bench in compara- 
