702 
Journal of Agricultural Research 
VoL XXIV, No. 8 
greenish gray/' respectively. Plate i8, Fg, represents a 12-septate 
spore of Helminthosporium sativum that was scraped from a wheat 
inflorescence and found to measure 134 /z in length, which may be 
regarded as approximating the maximum for this dimension. The 
maximum width represented, for example, in the spore shown in Plate 
18, Fe, is approximately 30 /z. The minimum for width of spore, as 
found in material occurring in nature, is about 14 /z (PI. 17, Ca), that for 
length in the region of 25 /z (PI. 18, Fc). When collected on diseased 
barley (PI. 17, Ca-i) or quack grass leaves (PI. 18, Ga-k) in midsummer, 
the spores are typically slightly or distinctly curved; 3 to 10 septate, 
widest near the middle, tapering slightly or sometimes quite considerably 
toward the ends which are rounded off abruptly, and show a hemis¬ 
pherical or hemiellipsoidal contour; and measuring usually 15 to 20 
by 60 to 120 /z. On wheat heads, (PI. 18, Fa-q), or on the bases of 
wheat or barley plants, apparently in response to more moist conditions, 
the spores are more apt to be atypical, being either straight or, if curved, 
curved irregularly (PL 18, Fd, f^ j); showing unusual variability in 
width, which fluctuates not only with respect to different individuals but 
also in respect to different portions of the same spore (PI. 18, Fi); exhibit¬ 
ing often marked irregularity in regard to septation, the septa occurring 
at unequal intervals, often at planes decidedly oblique to a plane per¬ 
pendicular to the longitudinal axes of the spore (PI. 18, Fk, n), and 
occasionally quite approximating a longitudinal position, thus bringing 
about a muriformly septate condition (PI. 18, Ff, h, i). The same 
departures from the curved, long-ellipsoidal type is exhibited also by 
spores developed on plants in the greenhouse and perhaps to an even 
greater extent by those produced in pure culture on artificial media. 
In the latter case the diminution in size is unusually great, the spores 
there (PI. 19, C, Da-c) generally not exceeding in length more than one- 
half the length of the typical ones to which, however, they are not 
markedly inferior in width. Very frequently, indeed, they become 
reduced to subspherical bodies, not appreciably greater in length than 
in diameter, often nonseptate or with a single cross wall (PI. 19, C). A 
straight, short ellipsoidal shape is thus characteristic of the spores 
developed in the greenhouse or in artificial culture (PI. 19, E), a shape 
which may be modified by irregular curvatures or distentions, or by the 
flattening or even incipient bifurcation of the apical end (PL 19, Dc). 
But, however variable in shape, the spores of Helminthosporium 
sativum^ when fully matured, are uniformly of a dark olivaceous color, 
and always exhibit a thick peripheral wall and a conspicuous hilum that 
is situated within the contour of the rounded basal end. As long as 
the peripheral wall is uninjured, gemiination regularly proceeds by the 
proliferation of two terminal germ tubes, one at the apex and the other 
immediately adjacent to the hilum (PL 17, Da, b; PL 18, Gc; PL 19, Da, 
b, d). Atypical spores, with the distal end flattened or bilobed, may 
produce three germ tubes, one arising from each of the lateral apices as 
well as from the proximal end. (PL 19, Dc.) Germ tubes apparently 
are never produced normally from the intermediate segments. Viability 
is retained for a considerable period of time, spores from material stored 
in the laboratory a whole year having been germinated by the writer 
without much difficulty. 
Helminthosporium sativum is very readily cultivated on the substrata 
ordinarily employed in laboratories. On hard potato glucose agar con¬ 
taining an abundance of organic food material the aerial growth is 
