Oct. 15,1925 Leaf spot of Maize Caused by Ophiobolus Tieterostrophus 703 
surrounding it. On some of the less mature foliage a purple tint 
was frequently evident in lesions that approached the Prussian Red 
of Ridgway's series. All except the very smallest lesions were 
elongated in a longitudinal direction, usually with the lateral edges 
characteristically straight and parallel and coinciding accurately with 
the course of the veins. Since the latter in the Florida material were 
spaced at intervals of 1.0 to 1.2 mm., and in the Philippine specimens 
at intervals of 2.0 to 3.0 mm., the lesions appeared generally as 
ribbonlike areas of corresponding width. In occasional instances 
two adjacent intervascular spaces were included in the dead regions 
and these consequently were double the usual width. The larger 
regions of discolored foliar tissue, however, had their origin less 
frequently in such lateral extension of single lesions than in the 
coalescence of numbers of lesions, side by side and end to end. 
Owing to the abundance of the spots, which numbered from 200 to 
300 on leaves not more than 50 cm. long and 2.5 cm. wide, the morbid 
parts naturally constituted a considerable portion of the foliar tissue. 
Under macroscopic inspection, the appearance of the leaves thus 
affected does not closely resemble that of specimens affected with 
blight, a well-known disease widely distributed in maize-producing 
countries and caused by Helminthosporium turcicum Passerini. The 
blight lesions are relatively few in number, usually not exceeding a 
dozen to an individual leaf, but their paucity is more than compensated 
for by their size; they are, when well developed, more thana nundred 
times larger than even the largest seen in the Florida material. A 
comparison of Figure 1, A, with Plate 24, A, in a previous publication of 
the writer ( 2 ) suggests the difference in number and size of the two 
types of lesions. Leaf-blight lesions show no indication of zonation 
other than a reddish-brown marginal border which often is not well 
developed or is even entirely suppressed. And while the portions of 
leaf killed by H. turcicum are also elongated longitudinally and often 
bounded on the sides by the veins of the host, more than one inter¬ 
vascular region are usually involved, the veins apparently providing 
a much less effective barrier to lateral extension than is evidenced 
in the specimens under consideration. 
CONIDIAL STAGE OF THE CAUSAL PARASITE 
Macroscopic examination revealed conidiophores and conidia typi¬ 
cal of the genus Helminthosporium scattered rather sparsely over 
the central portions of the larger lesions, the constant positional 
association strongly suggesting the causal relation subsequently 
established by inoculation experiments. On the material as obtained 
from the field, the conidiophores exhibited no unusual peculiarity. 
Singly, or in groups of two or three, they were found to emerge from 
the stomata (fig. 1, Da to De), resembling in the latter detail the 
homologous structures of H. turcicum; although such limitation to 
stomata is regarded as due to the mechanical firmness of the maize 
epidermis rather than to an inherent characteristic of the parasites 
concerned. However, a conspicuous difference distinguishing them 
from the conidiophores of the leaf-blight fungus was their smaller 
diameter, in which dimension they were found to measure usually 
from 4.5 to 7.0 n instead of 7.5 to 9.0 /x recorded for the other form. 
In length the conidiophore of the field material measured between 
120 and 170 /x, while scars marking the former points of attachment 
