80 BULLETIN 934, U. S. DEPARTMENT OF AGRICULTURE. 
infusion as in the inoculated pots not so treated. In the first experi- 
ment 5-pot units of unhealed soil were also inoculated in the same 
way. In these also both the units which received infusions showed 
less germination and more loss after germination than the unit which 
received no infusion, though the differences were smaller than in the 
autoclaved soil. In the second experiment the light inoculation used 
failed to cause material loss in the unheated soil units, even though 
two of them were treated with the infusion as in the previous test 
and two others received triple portions of the infusion. 
The experience in the nurseries, in which heavy applications of 
manure, and especially poorly rotted manure, in a number of cases 
have apparently resulted in increased disease, and the finding of 
Fred (43) that green manures recently plowed under favored the 
work of Corticium have already been mentioned. The addition of 
dried blood at two nurseries in Kansas was in both cases followed 
by very much heavier loss than in the controlled plats. The only 
instances known to the writer in which the addition of organic 
matter to the soil has shown any indication of materially decreasing 
damping-off (with the exception, of course, of the organic disin- 
fectants) are the result reported by Gilford (46) with tankage, a 
single case in the writer's experience with bone meal, and the cases 
in which cane sugar has seemed to decrease losses somewhat (67). 
It is of some interest to note that the experience available also indi- 
cates increased disease as a result of the addition of inorganic nitrog- 
enous substances. Sodium nitrate and sodium nitrite have both 
given some indication of increasing damping-off. Ammonium sul- 
phate in six separate series has in every case resulted in decreased 
stands, though unfortunately in experiments in which the damped- 
off seedlings were not counted. Ammonium hydroxid, though ap- 
parently having some initial value as a disinfectant, as indicated by 
early damping-off losses, in a number of cases has been followed by 
very heavy total losses. This experience is of some interest in view 
of the apparently rather general belief that plants on a soil rich 
in nitrogen are especially susceptible to disease. 
The chemical factor for which there is perhaps the most evidence 
of a relation to damping-off of conifers is acidity. The fact that 
sulphuric-acid soil treatment has been found to be one of the most 
effective means of controlling the disease, that its value is mainly 
lost if lime is later added to the soil, that soil treatment with sulphur 
in a number of cases has seemed to decrease the disease, and that 
lime alone and wood ashes have had either no effect or have appar- 
ently increased the damping-off whenever they have been tried, all 
suggest that soil acidity is not favorable to the disease. Additional 
indication of this appears in figure 12. The acidity determinations 
serving as the basis for the graph were made by Dr. L. J. Gillespie, 
