724 
Journal of Agricultural Research 
Vol. XXIV, No. 8 
diameter of its spores. Nor does it appear possible on morphological 
grounds to identify it with other species of Helminthosporium, including 
the numerous saprophytic types that have been referred to the genus. 
The specific name rostratum is suggested as descriptive of a conspicuous 
feature characteristic of many of the conidia. 
DIAGNOSIS 
Helminthosporium rostratum, n. sp. 
Occurring on the dry leaves of Eragrostis majory Host. 
Conidiophores dark olivaceous, emerging singly or in groups of 2 to 5 from stomata 
or between epidermal cells, the swollen bases ^ten more or less united; meastuing 6 
to 8 by 40 to 180 jLi; I to 6 septate, the septa separated by intervals of 15 to 40 /*; pro¬ 
liferating the first spore 40 to 140 /i from the base, and successive spores at intervals of 
10 to 30 Hy at the apices of well-defined geniculations. 
Conidia, when mature, dark olivaceous; straight or less frequently somewhat curved; 
often short, widest at or somewhat below the middle, tapering moderately or more 
markedly toward both ends, the hemi^herical apex abruptly rounded off, the basal 
end somewhat more acute, often exhibiting a rounded conical contour; or less fre¬ 
quently produced at the tip into a more or less elongated rostrate prolongation. The 
elliptical spores 3 to 9 septate, the rostrate types usually 8 to 15 septate, the proximal 
cross wall occasionally associated with a perceptible constriction in ^e peripheral 
wall. The basal septum ofteU, and the distal septum less frequently, appearing darker 
and thicker than the intermediate cross walls, such modification not unusually asso¬ 
ciated with a more dilute coloration of the delimited basal or distal segments. Peri¬ 
pheral wall thick except in two small subhyaline regions, one at apex, the other sur¬ 
rounding the conspicuously protruding hilum at the base. Mature spores germinat¬ 
ing by Ihe production of two polar germ tubes, one from each of the subhyaline thin- 
walled regions; immature spores often producing germ tubes also from intermediate 
segments. Measuring 14 to 22 ju in diameter W 32 to 184 n in length. 
Habitat. —Collected near Washington, D. C., September and October, 1921. 
HELMINTHOSPORIUM ORYZAE B. db H. 
Helminthosporium macrocarpum of von Thiimen not Greville. 
Helminthosporium oryzae Miyabe & Hori 1901, in N6ji Shikenjo H6koku, no. 18, p. 67-81. 
Probably the earliest record of the occurrence on rice of a species of 
Helminthosporium resembling the form now recognized as a widely 
distributed parasite on this cereal may be credited to von Thumen {150 ). 
This writer in a paper published in 1889 reported Helminthosporium 
macrocarpum Grev. as not infrequently appearing indiscriminately on 
dead parts of rice plants immediately after the tissues involved have 
ceased to live. To Che presence of the fungus was attributed a discolored 
appearance of the crop ^at had occasioned popular discussion of “attack'' 
and “ sooty mould." Von Thumen believed ^at the fungus nevertheless 
is not the cause of any disease, but that it makes its appearance rather 
as the result of disease or as a saphropyte accompanying entirely normal 
maturation. 
While the various saprophytic organisms that have been referred to 
Helminthosporium macrocarpum by different authors in all probability 
are not specifically identical, it may be assumed that such reference 
implies a moderately close correspondence to the diagnosis of Greville's 
species. In most details, indeed, this diagnosis is not widely at variance 
with descriptions of the fungus causing leaf spot of rice. A significant 
departure is evident, however, in the width of the sporophore, which in 
H. macrocarpum measures 15 to 20 /i, thus equaling or slightly exceeding 
the diameter of the conidia. The identity of the fungus observed by 
von Thumen thus is rendered somewhat doubtful. In any event it 
seems clear that no useful purpose could be served by associating 
Greville's binomial with the parasite on rice. 
