20 BULLETIN 169, U. S. DEPARTMENT OF AGRICULTURE. 
the time of germination is when acid applied to the beds will do the 
most damage to pine seedlings. The longer the period before or after 
germination takes place that the acid is applied the less danger there 
is of acid injury. The free acid in the soil solution would normally 
be decreased by diffusion or leaching downward into the subsoil, by 
adsorption or solid solution by the soil, and by chemical interaction 
with other constituents of the soil or soil solution. No attempt has 
been made to determine the relative importance of these different 
processes in the removal of the acid from the solution. It has seemed 
rather surprising that even with applications of acid as small as 0.25 
ounce per square foot enough acid remains free in the surface soil 
three weeks after application to kill the tips of jack-pine roots and 
prevent the growth of most dicotyledonous weed species for 1^ months. 
In soil containing large quantities of carbonates there could be no such 
length of persistence of free acid. 
The amount of injury occurring in plats treated at different lengths 
of time before germination and the comparative lack of relationship 
between the amount of acid used and the extent of injury in cases 
where more than 15 days elapse between treatment and germination 
indicate that the rate of dissipation of the free acid in the soil solution 
decreases rapidly as the concentration decreases. Very small 
amounts of acid have proved extremely injurious to root tips in the 
soil at the time of application. While they lose this extremely toxic 
character in a very few days after application, the final reduction to 
a point where no injury occurs requires a relatively long time. The 
apparent relative stability of very low concentrations of acid in the 
soil solution is in agreement with the general course of removal of a 
solute either by diffusion or chemical reaction. 
ADDITION OF NEUTRALIZING AGENTS AFTER THE APPLICATION OF THE ACID. 
In different experimental series, plats treated with sulphuric acid 
before sowing were later treated with neutralizing agents to prevent 
acid injury. This procedure greatly decreased the effectiveness of 
the acid treatment against the damping-off parasites on whose 
account the work was being conducted, and so it was not exhaustively 
tested. In no case was lime applied to the extent of equivalent 
weights of the acid used. 
The indications are that injury to pines may be prevented by small 
amounts of lime put on the beds a few days after the application of 
the acid. The results of the treatments are given in Table V. 
