4 BULLETIN 44, U. S. DEPARTMENT OF AGRICULTURE. 
occur in such distinct patches; and if any part of a transplant is 
affected, either an entire branch or the entire plant dies at once. — 
A feature of sun scorch in nurseries, as well as in the older trees 
described by Stone,' is that the absorbing portions of roots die at the 
same time as the tops or even before. This indicates that the leaf 
and stem tissues can stand water loss better than the vegetative 
tissues of the roots. Especially in the case of transplants the cam- 
bium of the entire root system, or at least of the outlying portions 
of it, has been found to be dead and brown. By the time the needles 
show the first signs of yellowing, a large part of the root cambium is 
already gone. This especially early death of a large proportion of 
the root systems of the scorched transplants is probably due to the 
fact that a tree in the transplant bed has a smaller root system im 
proportion to its transpiring surface than a second-year seedling 
would have. When only a part of the needles on a plant are killed 
it appears that the damage to the root is more extensive than to the 
tops. This is indicated by the fact that a plant which has lost part 
of its needles in an attack of this disease is more likely to succumb 
to later attacks of the same nature. Evidently the reduction in 
transpiring surface caused by the first attack is more than counter- 
balanced by the reduction in absorbing surface. 
During several sun-scorch attacks at Halsey, and at two or three 
other times when the weather was hot and dry but no actual sun 
scorch had occurred, a peculiar type of injury appeared on young, 
growing shoots of second-year pine seedlings. White, shrunken, 
watery-looking patches appeared on the green stems rather suddenly, 
followed by the death of the plant beyond the point attacked. A 
very similar “ white-spot” injury, occurring near the bases of the 
stems of seedlings less than a month old at the Halsey nursery, and 
which has often been confused with damping-off, can be controlled 
by shading and watering. While a parasite may be in some way 
concerned in causing the trouble in both ages of stock, there is little 
doubt that drought and possibly also excessive light or heat working 
independently are mainly responsible. This white-spot injury to 
second-year seedlings is included under sun scorch because it often 
occurs simultaneously and can be prevented by the measures which 
prevent scorch. It is not important. 
EVIDENCE AS TO CAUSE OF SUN SCORCH. 
The conclusion that the disease is due to disproportionate water 
loss is based on the following facts: 
(1) Spraying with fungicides has failed to control the trouble. 
While spraying experiments have not been exhaustive, Bordeaux 
1Stone, G. E. Sun scorch of the pine. Massachusetts Agricultural Experiment Sta- 
tion, 22d Annual Report, pt. 2 [1909], p. 65-69, 1910. 
