May 26, Z923 
. Graminicolous Species of Helminthosporium 
667 
teres and H, gramineum. The differences between the latter two species 
are, in reality, altogether much larger. For example, while the largest 
spores of the fungi causing netblotch and leafspot of oats, seen by the 
writer, have measured between 170 and 175 the longest spores of the 
stripe fungus have not been found to exceed 105 ix in length. The number 
of septa in the spore of the stripe fungus very rarely exceed 7, while in 
the other two species 8 and 9 cross walls may be found quite readily and 
even 10 or ii occur in a small proportion of instances. Production of 
secondary spores, common in H, gramineum^ is rare in H. avenae or H. 
teres. In short, H. gramineum is not closer to either H. auenae or H, 
teres than a moderate number of other congeneric species. 
As leafspot usually is not a serious disease, and in the United States 
not very conspicuous in its manifestations, little attention has been paid 
to its control. Atanasoff and Johnson (5) have found the hot-air seed 
treatment effective in reducing the disease. The value of methods of 
control based on seed disinfection would appear to be contingent, at 
least to some extent, on the absence of a possible sclerotial or ascigerous 
stage, or the relative ineffectiveness of such a stage as a factor in the 
propagation of the fungus. 
HEI/MINTHOSPORIUM TRITICI-REPENTIS DIEDICKE—PYRENOPHORA 
TRITICI-REPENTIS (DIED.) 
Helminthosporium gramineum Rab. f. sp. tritici-repentis Diedicke olim 1902, in Centbl. 
Bakt.[etc.] Abt. 2, Bd. 9, p. 317-^29. 
Pleo 9 pora tritici-repentis Died. 1903, in Centbl. Bakt.[etc.] Abt. 2, Bd. ii, p. 52-59. 
Pleospora trichostoma (Fr.) Wint. f. sp. tritici-repentis Noack 1905, in Ztschrif Pflanzenkr., 
V. 15, p. 193-205. 
Helminthosporium triticirrepentis as recognized by Diedicke (28) , first, 
as a biological or form species of H. gramineum Rab. and later (29), as an 
independent species, distinct from H teres y H.hromiy H, gramineum, and 
H. avenae. It appears to be widely distributed, its perithecial form 
occurring very abundantly in our northern latitudes on the dead culms 
of quack grass, Agropyron repens. The visible effects resulting from the 
attack of the fungus on growing plants of quack, grass are usually not 
at all conspicuous, any dark discoloration like ^at induced by the 
parasitism of H. sativum on the same host, being absent. The affected 
leaf gradually loses its green color and withers from the tip downward, 
changing at the same time first to a pale yellowish, and later to a gray 
color. As the foliage of the host developed after the earlier stages of 
growth is relatively rigid, the mechanical distortion associated with the 
death of any except the lower and more delicate leaves (PI. 5, A) usually 
is not very noticeable. 
According to Diedicke, the disease resembles barley stripe in affecting 
the whole plant, usually suppressing the development of the inflorescence, 
or preventing its emergence from the enveloping sheath. Although 
this opinion is not without some plausibility, anatomical evidence regard¬ 
ing the distribution of the fungus in the tissues of the plant would appear 
to be necessary before the disease can be regarded as systemic in the 
same sense as stripe. Some differences in the manifestations of the two 
diseases certainly are apparent. The symptoms do not become evident 
simultaneously in all the leaves of individual quack-grass plants, but 
are manifested first in the basal leaves, and later may appear in suc¬ 
cessively higher foliar organs. Nor do diseased leaves of Agropyron 
repens exhibit anything similar to the longitudinal variegation diar- 
