6 The Colorado Experiment Station 
sufficient vitality, throw out a good growth for the second and 
third cuttings. Strange as it may seem, there is little or no trace of 
the blight during the remainder of the season, but in the following 
spring, a renewed outbreak may be looked for. The severity of the 
attack seems to vary from season to season. As has been noted 
before, the trouble was moderate in 1904; in 1905 it was practically 
unseen; in 1906 and 1907 it was extremely bad; in 1908 the attack 
was mild and during the past year there was but little to be found. 
This season the crop was the best that has been harvested for four 
years. This variation in the degree of the attack would seem to in¬ 
dicate that there may be some relation between the prevalence of 
the disease and the weather conditions, especially late frosts and late 
freezing, intermingled with warm, pleasant days as compared with 
a late, cold spring. Not many plants are killed the first year, bur 
they begin to die after the blight has been prevalent more than one 
season, and after three or four years so many of them may be miss¬ 
ing that the stand is practically worthless. 
CAUSE OE THE DISEASE. 
If a small piece of the yellowish green, watery tissue from 
a diseased plant, it matters not whether it be stem or leaf, is placed 
in a drop of clean water on a glass slide, there will appear on all 
sides of it, after half a minute, a dense, milky cloud, which can 
be seen readily with the naked eye, and which slowly diffuses out 
into the drop. When this preparation is examined under the low 
power of the microscope (Leitz Objective No. 3, Eye Piece IV.) 
this milky zone easily resolves itself into swarms of bacteria, which 
under the high power (Leitz Objective No. 7, Eye Piece IV.) can 
be distinguished as actively motile rods, relatively short and thick, 
with rounded ends and occurring for the most part singly and in 
twos. 
If the surface tissue is removed and a portion of the deeper 
layers is examined, identically the same results will be obtained. 
If a fragment of the dried exudate is likewise placed in a drop of 
water, the whole gradually disintegrates and becomes a milky cloud, 
which under the microscope is a mass of motile bacteria. 
Now, if stained films are made from the milky cloud of any 
of the above preparations, using aqueous fuchsin, one invariably 
finds a practically pure culture of a short, medium thick bacillus 
with rounded ends, and with a tendency to stain darker at the poles 
than in the middle. 
Nutrient agar plates, prepared from any of this diseased tissue 
or from the dried exudate, and incubated for 72 hours at 28° C., will 
give, almost invariably, a pure culture of a smooth, glistening, gray¬ 
ish white colony, slightly raised, round, margins entire or undulat¬ 
ing, and concentrically ringed. 
