May 26,1923 Graminicolous Species of Helminthosporium 669 
covered with leaves or other rubbish, it often is entirely suppressed. 
There can be little doubt that the environmental factors of temperature 
and moisture are of primary importance in this connection. 
Diedicke recognized this perithecial form as a new species, Pleospora 
tritici-repentis, which he distinguished from Pleospora hromi largely 
because of the smaller dimensions of its perithecia, asci, and spores, and 
because of the failure of reciprocal inoculations to produce infection. 
Noack (95) did not accept the taxomonic dispositions made by Diedicke 
but regarded the perithecia on Bromus asper and B. inermis as not dif¬ 
ferent morphologically from those on Agropyron repensy or from the 
perithecia on barley presumably associated with the stripe fungi. He 
consequently reduced the parasites on quack grass and on the two 
species of Bromus to biological forms of Pleospora trichostoma (Fr.) 
Wint., which, like Diedicke earlier, he identified as the ascigerous stage 
of Helminthosporium gramineum. The fungi under consideration were 
accorded a dubious status in the general works published subsequently, 
like those of Lindau {83) and of Stevens {139). 
A comparison of material collected by the writer near Madison, Wis., 
in the spring of 1920, showed the general correctness of Diedicke's 
statements regarding the relative sizes of the perithecia and asci of 
Pyrenophora tritici-repentis and Pyrenophora bromi.. As the diameter of 
the perithecia of the parasite on quack grass appears to vary from 0.20 
to 0.35 mm. the inequality in size between the fruiting bodies of the 
two forms certainly is not pronounced. In Pyrenophora tritici-repentisy 
especially when developing on decaying leaves, the ostiolar beak usually 
is narrower, less massive, and consequently a somewhat more distinctive 
structure than in Pyrenophora hromi. The asci (PI. 6, C) of Pyrenophora 
tritici-repentisy measuring usually from 170 to 215 by 43 to 50 /i, are 
similarly somewhat smaUer than those of Pyrenophora hromi. 
It may be mentioned that measurements of asci in fully matured 
living material are dependent to a considerable extent on the amount of 
moisture present, as these structures under dry conditions usually are 
found contracted tightly over the spores, while under moist conditions 
they swell until the space inside of the fruiting bodies is completely 
occupied. In any case, on being crushed out of the perithecia, they 
undergo very considerable swelling preliminary to the rupture of the 
ascus wall and the discharge of the eight ascospores. The latter, of a 
brownish color and measuring usually 18 to 28 by 45 to 70 /x, are uni¬ 
formly three times transversely septate, often with one or both of the 
middle segments further divided by a longitudinal wall. The septa are 
associated with constrictions in the peripheral wall of the spore, which 
frequently is found enveloped in a gelatinous covering. (PI. 6, Da, Db, 
Eb.) 
Germination takes place promptly by the production of a germ tube 
from several or all segments. (PI. 6, Da-b.) On media ordinarily 
employed in laboratories, like potato agar, a fairly compact mass of 
white aerial mycelium is produced, corresponding in all respects to the 
growth obtained by the use of conidia. Anastomosis with the resultant 
production of groups of inflated lobulate segments is abundant in the 
submerged mycelium, but large sclerotia or imperfect perithecia of a 
size readily visible to the naked eye, like those produced by Helmintho¬ 
sporium hromiy have never been observed in pure cultures of H. tritici- 
repentis. 
