May 26, 1923 
Graminicolous Species of Helminthosporium 
673 
the first leaves that arise from the overwintering rootstock of B, inermis 
have barely completed their development before thay begin to show 
the scattered spotting characteristic of its attack. (PI. 8, Ab-c.) Each 
spot originates as a minute dark brown or black speck about which the 
chlorophyll gradually appears to break down, producing a yellowish or 
nearly colorless halo. Both the central spot and the surrounding zone 
usually increase considerably in extent, especially in a longitudinal 
direction, until the former may occupy an area 2 mm. in width and 6 mm. 
in length. On badly infected leaves the yellowed zones frequently run 
together as shown in Plate 8, B. Even more moderate infection, how¬ 
ever, leads to a premature withering of the leaf (PI. 8, Ad), beginning 
at the tip and proceeding downward, until the whole structure may be 
involved; for although the sheath is much less frequently spotted, it is 
not entirely immune, especially while the plant is still very young. 
After the leaf has become withered the sporophores make their appear¬ 
ance, first on or near the darkened areas, but later quite generally over 
the entire leaf. Emerging singly or in clusters of two (PI. 8, Ea-c), 
most frequently between epidermal cells without much reference to 
the stomata, they measure 7 to 10 /i in diameter and usually 100 to 150 ^ 
in length, although sometimes attaining a maximum length of 250 /i. 
From 2 to 6 septa usually are present. The geniculations associated 
with the production of successive spores are not generally very pro¬ 
nounced. 
In the account given by Diedicke {28) the spores are described as 4 
to 6 septate, 108 to 150 ju long, 13 to 20 ju in diameter, and exactly 
similar to those described and figured by Ravn (115), the supposed simi¬ 
larity presumably applying to Helminthosporium teres. Such a state¬ 
ment of the morphological features of the spores of the two species, it is 
quite impossible to substantiate by a comparison of American material, 
which reveals instead very decisive differences. The contrast in length 
between the two species is especially conspicuous, the spores of H, hromi 
measuring from 45 to 265 ju in lenglli, examples exceeding 200 /x in length 
being of not uncommon occurrence. (PI. 8 Ca-f.) Some difference in 
diameter also is perceptible, although this is much less pronounced, the 
spores of H. hromi varying commonly from 14 to 26 /x. As the number 
of septa in the spores of both species varies from i to 10, it is apparent 
that the individual segments in the spores of H. hromi exceed in length 
those of H, teres in approximately the same measure as do the spores. 
In H, teres, moreover, the spore often is conspicuously constricted at the 
septa, a modification absent or less strongly pronounced in those of H, 
hromi (PI. 8, De). Related to these features are the specific peculiarities 
in the contour of the basal cell that have been mentioned in another 
connection, this contour being approximately hemi-ellipsoidal in H, 
hromi and hemispherical in H, teres. 
In the conidia of Helminthosporium hromi, the hilum is represented 
by a scar, not especially conspicuous, and included entirely within the 
contour of the peripheral wall. As the peripheral wall consists of a 
relatively thin membrane, it is not surprising that the conidia show little 
resistance to unfavorable conditions. Even in actively sporulating 
material, microscopic examination reveals one of several dead segments 
in most of the spores, and when material is kept in the laboratory the 
proportion of dead segments or dead spores is very greatly augmented 
in the course of a week. hen mounted in water, viable spores germinate 
39365—23-3 
