May 26 , 1933 
Graminicoious Species of Helminthosporium 
721 
from 2 to 4 mm. in width, were found in an entirely collapsed condition. 
(PI. 28, B.) The absence of any indication of discoloration and the 
entire loss of mechanical stiffness combined to present an appearance 
such as might be brought about, for example, by scalding with boiling 
water. Soon after the wilting became visible, Bie portions of leaf in¬ 
volved dried out completely, becoming somewhat shrunken, dark in 
color and^ crisp in texture. Usually the death of the entire leaf blade 
ensued within a week, as much apparently because of the interruption 
of the vascular elements by the enlargement and multiplication of in¬ 
fected regions as because of the extension of the trouble to healthy parts. 
On the older leaves the disease was found less destructive, the injury 
tending to be restricted to more definitely circumscribed elliptical spots, 
varying from 2 to 10 mm. in length, and not infrequently delimited by a 
brownish margin. Nevertheless, these older leaves likewise slowly 
succumbed, the withering beginning at the tip and gradually progressing 
toward the base. 
On examining the dead foliage under the microscope, it was found 
that the regions involved in the lesions bore numerous fructifications of 
a well defined species of Helminthosporium. The first conidiophores to 
appear after the death of the tissue seemed usually to emerge from the 
stomata (PI. 28, Ea-g), although later they could be found emerging 
between epidermal cells as well. Except that the sporophores are 
smaller in diameter than might be expected from the size of the spores, 
they exhibit no distinctive Aaracteristic. 
The conidia (PI. 28, Ca~m) on the other hand are decidedly charac¬ 
teristic and can be readily distinguished from those of any congeneric 
species which the writer.has examined. Generally subhyaline or slightly 
fuliginous, they resemble in respect to coloration the spores of Helmintho- 
sporium teres^ H, hromiy H, giganteuniy and H. tritici-repentis. Unlike 
the conidia of any of these fimgi, however, they are typically more or 
less curved, a fact which together with the mode of germination by the 
production of two polar germ tubes (PI. 28, Da-c) suggests comparison 
with H. leersiiy H, cynodoniiSy and H. turcicum. From the spores of the 
ftmgus causing leaf blight of maize, those of the parasite on Paspalum 
boscianum are readily distinguished by their smaller dimensions, a very 
perceptible difference obtaining in respect to length and diameter. As 
the number of septa in the conidia are approximately equal, or even 
somewhat greater in the fungus thriving on P. hoscianuniy a very pro¬ 
nounced difference in massiveness between the spore segments of the 
two species is readily apparent. In general shape, the conidia of the 
parasite on Paspalum boscianum are less inclined to taper toward the 
ends than those of the H, turcicumy frequently all the segments except 
the terminal ones being of nearly the same diameter. The most char¬ 
acteristic feature, however, is found in the shape of the proximal end of 
the spore, which tapers quite abruptly and uniformly from the basal 
septum into a nearly cylindrical short prolongation, terminating abruptly 
in the flat hilum. Because of this curious modification, the contour of 
the peripheral wall usually exhibits a slight, barely perceptible, reen¬ 
trant curve. 
Among the species of Helminthosporium discussed in this paper the 
form on Paspalum boscianum is altogether unique in causing under 
natural conditions a violent wilting effect on the tissues of its host. The 
only instance known to the writer of similar pathological symptoms 
attributable to a congeneric species is the wilting produced experi- 
39365—23-6 
