4 
Journal of Agricultural Research 
VoL XIV, No. x 
Stage 7.—The older leaves are practically disintegrated, with noth¬ 
ing but the petioles remaining. The younger leaves are brown, with no 
evidence of green and very little yellow color. The plant at this stage 
has reached a point of low vitality, but life still continues in the younger 
leaves and crowns. This is shown in Plate 5, B, a. 
Stage 8.—The plant is dead, but has not entirely disintegrated 
(PI. 5, B, b). At this stage a plant which was perhaps 15 inches in di¬ 
ameter before it was attacked by the disease is reduced to a small whorl 
of leaves scarcely an inch in diameter. 
The root is apparently healthy and performs its normal function until 
the fourth stage is reached. From the fourth to the eighth stage the 
root gradually declines from the normal appearance. The root of a 
diseased plant is characterized by its shrunken appearance, a loss of 
lateral rootlets, and a browning of the internal tissues. This would 
indicate that the disease affects the foliage and aerial portions of the 
plant rather than the roots, the effect on the roots in all probability being 
secondary. 
THE LENGTH OF THE VARIOUS STAGES 
A more or less definite length of time elapses between the appearance 
of the first symptoms of the disease and the death of the host. In order 
to determine the length of the life cycle of the diseased plants under 
field conditions, the following experiment was performed. 
Forty-one healthy and diseased plants were staked in the field on 
February 9, 1917. Records were made of the condition of the plants 
and the stage of progress of the disease. They were examined on Feb¬ 
ruary 22, March 3 and 22, April 2, 10, and 25. Each time records were 
made of the condition of each individual plant. The results of these 
observations are shown graphically in figure 1. The incubation period, 
or the time elapsing between inoculation and the appearanee of the first 
symptoms under field conditions, was determined from the inoculation 
experiments. The average time between the inoculation and the death 
of a spinach plant is 81.75 days, and the disease progresses gradually 
from the appearance of the first symptoms until the plant is dead. The 
slight variation shown in the length of the different stages is probably 
due to the variations in the time the observations were made. Theoreti¬ 
cally the line representing the progress of the disease* would be straight. 
HISTORY OF SPINACH-BLIGHT 
Spinach-blight was first observed at Lambert’s Point, Norfolk County, 
Va., about 13 years ago and has since spread throughout the entire 
section. 
Prior to 1907 spinach-blight had become so serious that spinach 
growers were asking for assistance in its control. The first experiments 
that were conducted with regard to the control of spinach diseases in 
Tidewater, Va., were undertaken by the Office of Cotton and Truck Dis- 
