10 BULLETIN 169,, U. S. DEPARTMENT OF AGRICULTURE. 
after the acid treatment (1 day before germination), and a number 
of seedlings were injured. It was evident from the results obtained 
that these heavy applications of water leached out enough acid mate- 
rially to reduce acid injury. Leaching is evidently not practicable 
as a method of preventing injury at most nurseries when germination 
is prompt. In a sandy soil when the weather is cold and germination 
requires 18 or 20 days, leaching soon after the application of acid 
may be a practicable method of preventing injury. 
PREVENTION OF INJURY BY FREQUENT WATERING. 
Fortunately two definite relationships which opened the way for 
developing a practicable method of controlling the injury to the 
pines were found. It was found that the amount of water in the soil 
at the time of germination bore a direct relation to the amount of 
injury, and that injury seldom occurred after the seedlings had sent 
their roots down five-eighths of an inch into the soil. The length of 
root shown in Plate I, figure 3, is typical of injured seedlings in 
general. The stoppage of growth of root apices in treated beds 
always occurred at times when the upper soil became relatively dry 
and while the root tips of germinating seedlings were still in the upper 
five-eighths inch of soil. Although the nurserymen water the beds 
often enough to prevent drought injury to the seedlings, great varia- 
tion in the moisture content of the surface soil occurs. The upper 
one-fourth inch of soil at this nursery just after watering has fre- 
quently been found to contain 21 to 25 per cent of moisture, while at 
the same points the soil when dry has contained but 1.96 per cent of 
water, the average of 12 determinations made on different occasions. 
In a single period of 11 hours the moisture content of the surface soil 
at four different points in the seed beds dropped from 12.02 to 1.85 per 
cent. This of necessity caused great variations in the concentration 
of the soil solution. While beds were not ordinarily allowed to 
become as dry as this during the germinating period, they often 
became quite dry at the surface. A little below the surface the mois- 
ture content of the soil is more stable. The most rapid loss of moisture 
found in the seed beds from 1 to 2 inches in depth during the period in 
which determinations were made was a drop from 17 to ll£ per cent 
in a period of approximately 36 hours. This explains the relative 
safety of roots which have penetrated below the upper half inch of 
soil. That the root above the tip should resist relatively high con- 
centrations of acid is in agreement with the results of Heald * and 
other investigators, who find the tip of the root to be the portion most 
sensitive to poisons. The difference in resistance between the very 
1 Heald, F. D. On the toxic effect of dilute solutions of acids and salts upon plants. In Bot. Gaz., 
v. 22, no. 2, p. 130, 1896. 
