666 
Journal of A gricuUural Research voi. xxiv. No. s 
rium diseases of barley. As a result, the damage to the oat crop due 
to leafspot, although undoubtedly not of major importance, is much 
more likely to be considerably underestimated than that caused by the 
majority of related diseases of other cereals. 'Thus, during the latter 
part of June, 1920, the oats observed by the writer growing in isolated 
patches in the eastern half of Long Island bore only meager evidence 
of being affected by leafspot. Nevertheless, four weeks later, micro¬ 
scopical examination revealed the fructifications and spores of H. avenae 
on more than half of the mature plants, sometimes in considerable 
quantity. 
After the death of the affected leaf, the red and orange pigmentation 
very largely disappears, being replaced by a pale-yellow or gray color, 
and even the brown discoloration usually loses some of its intensity. 
At this point the conidiophores of the fungus make their appearance. 
As Ravn has pointed out, these structures (PI. 4, Da-g) are very similar 
to those of Helminthosporium teres in all respects—color, dimensions, 
septation, and mode of emerging from the epidermis—although exhib¬ 
iting sometimes a slightly greater tendency toward occasional branch¬ 
ing (PI. 4, Dc, De). The spores also resemble those of H, teres very 
closely, having approximately the same range in size and number of 
septa; and showing the same irregularly cylindrical shape, hemispherical 
ends, subhyaline to light fuliginous coloration, and mode of germination 
by the production from intermediate as well as end segments, of laterally 
or obliquely oriented germ tubes. 
The writer was unable to confirm Ravn’s finding that the conidia of 
H. avenae slightly exceed in length those of H, teres. In general, the 
dimensions of the two species appeared quite equal, and whatever slight 
inequality in length and width was observable was rather in favor of 
H. teres. It must be mentioned, however, that the fresh material used 
by the writer in the study of the two forms was not developed under 
comparable conditions, that of H. teres having been collected late in 
October during a damp, cool period seemingly especially favorable for 
sporulation; while the material of H. avenae, collected late in July, had 
manifestly developed at midsummer temperature. Perhaps the two 
fungi might better be regarded as biological forms of the same species, 
in the same sense in which such forms are recognized in Puccinia graminis 
and in the mildews. Whatever slight morphological differences, demon¬ 
strable in the conidial stage by biometrical methods, may exist between 
the two fungi, they could scarcely be of a larger magnitude proportionally 
than the differences between various biological forms of, for example, 
the stem rust fungus. A study of the ascigerous form of H. avenae, 
which, as has been suggested, the writer believes he has collected, although 
in very poor condition, ought to cast some light on its taxonomic relation¬ 
ship. For the present, it is advisable to follow Eidam and Ravn in 
regarding the parasite on oats as distinct from H. teres. Certainly the 
idea, proposed by Briosi and Cavara, of placing it as a morphological 
“forma of H. teres is not tenable. 
It may not be amiss to call attention to an error apparently caused by 
a partial misinterpretation of Ravn's paper, and more particularly of his 
widely copied but, perhaps, insufficiently representative figures of the 
conidia and conidiophores of Helminthosporium gramineum, H. teres, 
and H. avenae. In some general treatises, the impression is conveyed 
that the possible morphological difference between H. avenae and H, 
teres is approximately of the same order as the difference between H. 
