May 26,1923 
Graminicolous Species of Helminthosporium 
659 
in the development of primary lesions in the field was shown by the 
virtual absence of such lesions from the first leaf of plants resulting from 
sowings made in July and the first half of August, in contrast to a high 
percentage of infection secured from sowings made in March and April. 
The prevalence of netblotch on volunteer barley in the northern latitudes 
of our Middle Western States, where the temperature in midsummer 
ordinarily is at least as high as in Denmark, is accordingly on a priori 
grounds not to be attributed to seed infection. And, indeed, the abun¬ 
dance of the lesions on the first few leaves of a large proportion ofvolunteer 
seedlings in the fields kept under observation by the writer in 1919 
indicated secondary infection due to spores from stubble and other 
remains of the regular crop. 
Barley leaves affected with netblotch usually are not difficult to 
distinguish from leaves attacked by stripe or spotblotch. The presence 
of the parasite in the living foliar tissues is manifested by the appear¬ 
ance of dark brown spots or streaks which at first may be barely per¬ 
ceptible, measuring perhaps not above i mm. in length, but later 
increasing considerably in size, although not frequently measuring more 
than 20 to 25 mm. in a longitudinal direction. The increase in width 
usually is relatively small. A variegated appearance simulating that 
of the foliage of ribbon grass, due to alternately placed green and yellow 
stripes, is never produced, although the brown streaks characteristic of 
the later intermediate stages of stripe may sometimes be approximated 
in leaves affected by Helminthosporium teres. The most distinctive 
feature of the discolored areas involved in netblotch lesions is to be 
found, however, in the irregular distribution of the brown pigment, 
the latter being accentuated in very narrow lines, some oriented longi¬ 
tudinally, others transversely or obliquely to the exis of the leaf. As a 
result, a more or less irregular dark brown reticulate pattern may be 
distinguished within the areas of diffused brown. (PI. 2, A, B.) Indeed, 
the pigmentation of the interstices within the reticulate pattern may 
become so reduced that the discoloration is present almost exclusively 
as a sharply defined network of brown lines. (PI. 2, B.) The resulting 
macroscopic appearance, utterly different from that characteristic of 
stripe or spotblotch, and duplicated (as far as the writer is aware) only 
in leaves of meadow fescue affected by H, dictyoides^ led Johnson (j) 
to apply to the disease the descriptive name ‘"netblotch,” which has 
since been generally adopted in the United States. The parts of the 
leaf immediately adjacent to the discolored tissue usually shows more 
or less etiolation that becomes manifest in the appearance of a nanrow 
yellowish zone surrounding the spots. (PI. 2, B.) Sometimes, especially 
in incipient lesions in which the reticulate character is pronounced, the 
measure of etiolation is apparently small, and the dark brown netlike 
l^nes are found in leaf tissue apparently very little changed. Later, 
however, all the lesions show yellow margins, which eventually become 
extended until the whole leaf blade is involved and withers from the 
tip to the base. (PI. 2, Ad, Ae.) At this stage the spots, which may 
number several score on a single leaf and often become more or less 
confluent, begin to fade from a dark brown to a more diffused dull 
brownish gray. Not much later the fructifications appear as a light 
efflorescence extending usually from the brownish spots over the sur¬ 
rounding yellowish gray portions of the dead foliar organ. 
The injury due to Helminthosporium teres, like that occasioned by 
most of its foliicolous congeners is thus the result of the destruction of 
