626 
Journal of Agricultural Research 
Vol. XI, No. xi 
light brown. Following infection, the invaded tissues sooner or later 
lose their normal green, passing through translucent yellowish to brownish 
tints. Translucency is indeed so constant and distinctive a character 
of the lesions, even in the later brown stage, as to suggest the specific 
name chosen for the parasite. 
If a leaf showing a strong, freshly developed invasion along the mid¬ 
vein and extending down the sheath (Pi. 47, B) is cut sharply across at 
the ligule and either portion squeezed between thumb and finger, a 
milky-gray droplet appears on the cut surface. Microscopic examina¬ 
tion of this droplet proves it to be teeming with bacteria. If such or 
similar lesions are cut across and mounted in water, the bacterial extru¬ 
sion may be readily demonstrated under the microscope. In a rather 
advanced stage of the lesion the slime expressed between thumb and 
finger as referred to above may be of the consistency of thick cream, 
and, when exposed to the air, quickly hardens to a brittle resinous mass. 
These facts are the more interesting since one of the distinctive char¬ 
acters of the disease is the occurrence in nature, under favorable con¬ 
ditions, of a bacterial exudate hardening thus upon exposure. Under 
humid conditions, especially in the early morning, such exudate may 
appear on either surface of recently invaded leaf tissues as tiny, clouded 
droplets. These differ from the ordinary droplets of guttation water in 
their distribution on the lesions, their smaller size, and in the fact that 
they are distinctly grayish or milky, whereas the guttation water is 
crystalline clear. If such exudate droplets remain undisturbed they 
soon harden into yellowish, resinous granules studding the surface of the 
lesions (Pi. 47, D), but are easily detachable. Frequently these droplets 
coalesce with each other or with the guttation water and form con¬ 
spicuous drops (Pi. 47, A) which later may spread over the leaf surface 
and dry down as a thin, grayish, almost transparent film (Pi. B, 3; 47, 
C, b). This exudate may occasionally be sufficiently abundant and 
sticky to entrap small insects (Pi. 47, C, a). It is noteworthy also that 
this dry exudate is quickly redissolved in water (PI. 48, A); and doubtless 
this characteristic aids materially in the dissemination of the organism 
as discussed later. 
Since the appearance of the leaves striped by this bacterial blight may 
sometimes resemble the Helminthosporium stripe disease, distinctions 
are worth noting as follows: (a) the Helminthosporium disease is 
systemic, striping usually all the leaves of the attacked host plant, 
whereas the bacterial attack is local; ( b ) the water-soaked and trans¬ 
lucent appearance, and (c) the exudate are peculiar to the bacterial 
blight. 
On The heads. —In case the flag leaf is badly attacked before the 
head escapes, the exudate may so seal up the sheath that the head can 
not escape (Pi. 49, A). In some cases the heads may emerge, but may 
be variously bent and distorted, and a portion of the grains blighted. 
