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



Halsey indicated a considerable variation in resistance to sulphuric 

 acid between species of these four phylogenetic groups, exceeding 

 the variation between different species in the same group. It further 

 appeared that, for the four main groups represented, the higher the 

 group in the evolutionary scale the greater the susceptibility of its 

 representatives to injury, not only by sulphuric acid but by hydro- 

 chloric and nitric acids and by some of the toxic salts. It is under- 

 stood, of course, that these differences would not be expected to 

 obtain with all species of these groups, and parallel water-culture 

 tests with the species observed by the writer would probably show 

 that some of the differences in susceptibility indicated in the nursery 

 tests were due to other factors than variable protoplasmic resistance. 

 The experiments reported in the foregoing were devised primarily for 

 developing disease-control methods, and interpretation of many of 

 the direct effects on the seedlings is of necessity difficult. 



From the practical standpoint, it seems probable that sulphuric 

 acid can not be used alone as a disinfectant for sandy soil soon to be 

 sown with truck crops. This is at least true if the plants to be grown 

 prove as susceptible to acid injury as the dicotyledonous weeds 

 encountered in these experiments seemed to be. However, acid can 

 probably be applied with safety on most soils several days before 

 sowing if air-slaked lime sufficient to counteract three-fifths or more 

 of the acid used is raked into the surface soil just before seed sowing. 

 Sulphuric acid is so much cheaper than formalin that if subsequent 

 lime neutralization is found practicable this acid may in many cases 

 supplant both heat and formaldehyde as a soil disinfectant for work 

 in which immediate reinfection with parasites is not feared. The 

 writer's experience indicates that, aside from the destruction of 

 parasites, soil treatment with acid followed by lime results in a 

 considerable increase in the growth of many plants, in some cases 

 being more prompt and marked than that following heat disinfection. 



SUMMARY. 



Sulphuric, hydrochloric, and nitric acids, and copper sulphate 

 used in disinfection of seed-bed soil caused injury to the roots of pine 

 seedlings and prevented the development of many species of angio- 

 spermous weeds. All cause injury to pines by killing the growing 

 apex of the radicle i mm ediately after the seed germinates. They 

 can be used to disinfect pine seed beds only if the operator knows how 

 to recognize and prevent such injury to the pines. Typical healthy 

 and acid-injured seedlings are shown in Plate I, figures 1, 2, and 3, 

 and a method by which injured seedlings can be distinguished from 

 others is described on page 9. Many injured seedlings later resume 

 root growth and recover (PI. I, fig. 4, and text figs. 1 and 2). Injury 

 is due to the concentration of the disinfectant in the surface soil 



