6 BULLETIN 4, U. S. DEPARTMENT OF AGRICULTURE. 
from the blighted area and two from the healthy, and determination 
showed 30 per cent more water in the samples from the healthy area. 
Altogether, samples taken at 10 different points in diseased stands 
during three different attacks gave an average moisture content of 3.4 
per cent for the soil from 2 to 11 inchesin depth. The average wilting 
coefficient of the soil at this nursery, determined from samples taken 
from the same depths at nine different points located in the same 
parts of the nursery as the moisture determinations above referred 
to, was 3.6 per cent, as determined by the indirect method of Briggs 
and Shantz from moisture-equivalent determinations made by the 
Laboratory of Biophysical Investigations. While the soil-moisture 
determinations made were too few to establish the relation of dry 
soil to the disease, they are to be viewed as contributory evidence. 
(8) High points in beds and the centers of arched beds from which 
the water runs off or which are missed in flood irrigation are espe- 
cially liable to damage from the disease. 
(9) Species which normally inhabit moist soil suffer most. Nor- 
way spruce (Picea excelsa Link) and Douglas fir (Pseudotsuga taxi- 
jolia (Poir.) Britt.) seem to suffer oftener than the pines. Western 
yellow pine (Pinus ponderosa Lawson) grown from Rocky Mountain 
seed is more resistant at Halsey than other pines. 
(10) Sufficiently frequent and heavy watering will entirely pre- 
vent the disease. In three different attacks at Halsey evidence of 
the preventive effect of watering was obtained. The main practical 
fact is that for two seasons the nurserymen at Halsey and at Monu- 
ment, Colo., have practically controlled the disease by increasing the 
frequency of watering. At these nurseries during the three preced- 
ing seasons the disease had caused considerable loss. At both these 
nurseries the disease had been considered parasitic. 
It is not thought that death is usually due to the entire lack of 
available soil moisture. It is rather probable that it usually occurs 
when there is still a certain amount of available water left in some 
part of the soil reached by the root system, but so small in quantity 
that it can not be taken up by the roots fast enough to supply the 
demands of the rapid transpiration loss from the needles. This does 
not necessarily mean slowness of imbibition; it may simply mean 
that the capillary water movement from outlying soil particles to the 
particles adjoining the root surface is too slow when the soil is nearly 
dry. That this is the case is indicated by the fact that after an at- 
tack of sun scorch has started as the result of one or two days of 
rapid transpiration, when the soil is quite dry, the disease may stop 
spreading on the advent of cooler weather without the addition of 
any water to the soil from above. 
Some interesting occurrences at Halsey in connection with this 
trouble. which at first appeared to contradict the relation of the dis- 
