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 f ollowing 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 immediately 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 (PL I, fig. 4, and text figs. 1 and 2). Injury 
is due to the concentration of the disinfectant in the surface soil 
