382 BROOKLYN BOTANIC GARDEN MEMOIRS 
. Poae upon Poa annua, P. trwialis, P. pratensis, P. caesia, P. 
mutalensis, P. nemoralis and P. serotina. 
. Agropyrt upon Agropyron. 
7. Bromi upon various species of Bromus. 
Salmon (123, 128) has infected Avena nuda, A. brevis and A. sativa 
with conidia from A. nuda; conidia from A. sterilis infected A. pratense 
and A. sativa; and conidia from A. sativa infected A. sativa, A. brevis, 
A. nuda, A. orientalis, A. sterilis and A. strigosa. Attempts to infect 
twelve other grasses, belonging to different genera, with the oat mildew 
failed. 
The writer (120) has carried out an extensive series of experiments 
with the powdery mildew on Avena sativa. Infection occurred on the 
following: A. barbata, A. brevis, A. fatua, A. fatua var. glabrata, A. 
ludoviciana, A. nuda, A. nuda var. chinensis, A. nuda var. elegantissima 
A. planiculmis, A. pratensis, A. pubescens, A. purpurea, A. sativa 
(sixteen varieties), A. sativa orientalis (six varieties), A. sterilis, A. 
strigosa and A. sulcata. In most cases, in a large number of trials, 
one hundred percent of infection was secured. The oat mildew also 
infected Arrhenatherum avenaceum. Negative results were obtained 
with Avena bromoides and A. sempervirens, as well as grasses belonging 
to other genera. This race, then, extends over a wide range of species 
and varieties of Avena, but, with the exception of Arrhenatherum 
avenaceum, is restricted to this genus. 
Salmon (123, 132) has reported only a few results with the powdery 
mildew of wheat. He successfully infected Triticum vulgare and T. 
Spelta with conidia from the former. He also states that young 
seedlings of Hordeum silvaticum could be infected with the same 
mildew. 
Vavilov (164) has tested out, under field conditions, seven hundred 
and fifty-five ‘‘pure-lines’’ belonging to the different species and 
varieties of Triticum. He used pure lines belonging to thirty varieties 
of Triticum vulgare, seven of T. compactum, ten of T. turgidum, nine 
of T. Spelta, fifteen of T. durum, three of T. polonicum, five of T. 
dicoccum and four of T. monococcum. In general the pure lines be- 
longing to the different varieties of 7. vulgare, T. compactum and 
T. Spelta are extremely susceptible to the mildew, while the pure 
lines of the varieties of 7. durum, T. turgidum, T. polonicum and 
T. monococcum proved, in the main, to be quite resistant. The pure 
lines of some varieties of T. dicoccum proved to be highly susceptible, 
while the pure lines of other varieties were markedly resistant. Dif- 
ferences in the susceptibility of the pure lines were noted and certain 
varieties, notably 7. vulgare var. fuliginosum and T. dicoccum var. 
picnurum stood out as distinctly immune. However, the pure lines 
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