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 unheated 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 Gifford (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, 



