6 BULLETIN 169, U. S. DEPARTMENT OF AGRICULTURE. 



cases resulted in lessening injury, presumably exerted its effect 

 through an immediate further dilution of the acid in the surface 

 layer of soil. While part of the apparent freedom of the aerial parts 

 of the plants from direct acid injury may be due to the slight tendency 

 of liquids to adhere to pine seedlings, drops of 1 to 256 acid solution 

 by volume (0.71 per cent by weight) frequently remained caught in 

 the center of the whorls of cotyledons of yellow-pine seedlings. 

 This localization of solution was not accompanied by any noticeable 

 localized injury. The experience of Craig, 1 indicating direct injury 

 to the foliage of grapes, plums, and apples out of doors by a solution 

 containing but 0.25 per cent of the acid, was more closely duplicated 

 in the case of seedlings of a grass resembling a common native species 

 of Panicum, which occurred in some of the plats. Definite character- 

 istic spots of dead leaf tissue were noted on the grass plants in a few 

 cases in plats treated with a solution of 1 to 512 by volume (0.36 per 

 cent). The solution adhering to the leaves is, of course, concen- 

 trated by evaporation of the water after application, so the injury 

 from spraying with solutions is actually caused by a much stronger 

 solution than that applied. 



The tests outlined in the foregoing statement indicate that after 

 the seed begins to germinate, any application of sulphuric acid suffi- 

 cient to affect materially the activity of the damping-off parasites 

 will cause the death of the radicles of some of the pine seedlings. 



In applications after the beginning of germination, the concentra- 

 tion of the solution applied, as well as the amount of acid used per 

 square foot, seemed distinctly related to the amount of injury to the 

 roots of the seedlings. This indicates that the injury occurred very 

 promptly after the application of the solution, before diffusion 

 between the upper and lower layers of soil had time to equalize 

 quantities and concentration of the soil solution. The younger parts 

 of the roots were still in the upper 1 or 2 inches of soil in most cases 

 at the time the injurious solutions were applied. 



INJURY TO PINES BY SULPHURIC ACID APPLIED AT THE TIME OF SOWING. 



In applications made at the time of sowing it was found that 

 stronger treatments could be given without injury to the pines than 

 when the treatments were delayed until germination. Stronger 

 treatments were also required in order to control parasitic fungi, so 

 that it was necessary in these tests also to work with treatments 

 strong enough to cause injury to seedlings. Because of the numerous 

 advantages of acid treatment at sowing, from the standpoint of 

 disease prevention and nursery practice, a detailed study of the 

 injury it causes to seedlings was undertaken with a view to pre- 

 vention. 



i Craig, John. Effects of dilute sulphuric acid on foliage. In Canada Exp. Farms, Rpt., 1893, p. 101- 

 102, 1894. 



