16 THOMAS: INFECTION OF APIUM GRAVEOLENS 
full with heavily diseased leaves and petioles of celery. Five pots 
were similarly filled with healthy green leaves. Celery plants 
were potted in garden soil in the upper part of these pots and 
twenty days later these plants were inoculated. The result was a 
very decided increase in infection upon the plants which received 
the diseased material (TABLE VI). While there was no perceptible © 
TABLE VI 
INFECTION ON PLANTS TREATED WITH DISEASED CELERY LEAVES IN THE SOIL 
| | Average 
Plant No, pot = eee | 5 | No. spots 
| | ce leaf 
Plants with diseased material | Spots per plant..... el es oe 361| I 53| 38.7 
Leaves per plant. | | 
Controls Spots per plant..... Irs9l 217 55|132/187| 19.7 
| Leaves per plant.. .| 13) 4 13 ib | ae Oa 
difference in the appearance of the two series of plants, the most 
reasonable explanation of these results is that the diseased material 
with decay already under way would supply, at the time of inocu- 
ation, a condition similar to that produced by the application of 
manure made in an earlier experiment. The depth at which the 
material was buried and the uniformity in time with which the 
infection appeared preclude the possibility of the action of this 
material as an additional source of inoculum. 
INFECTION OF PLANTS INFESTED BY NEMATODES 
Perhaps the most conclusive data bearing on the relation of 
health to infection were obtained incidentally in the course of 
experiments planned for other purposes.. Twelve plants which 
had received various treatments were given two successive 
inoculations, which produced at most only a few spots. These 
were finally thrown out and the roots were found to be heavily 
infested by nematodes. Again nine plants were set aside from a 
variety test as possibly resistant individuals. These were also 
found to be infested. The infection (Septoria) on these plants is 
compared with that on two non-infested plants of the same experi- 
ment in TABLE VII. So far as thesg,observations extend, nema- 
todes do not develop to any markt, degree on any except badly 
pot-bound plants. However, a number of galls may be produced 
_ on the roots of plants in fairly good growing condition. A number 
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