ijl 
REED: SPECIALIZATION OF PARASITIC FUNGI 381 
results: (1) conidia from Artemisia vulgaris, Lactuca muralis and 
Lithospermum arvense infected plants of the same species but did not 
infect each other nor some other plants tested; (2) conidia from 
Eieracium murorum infected H. murorum and Leontodon taraxacum, 
the latter very slightly; (3) conidia from Senecio vulgaris infected 
S. vulgaris and Lactuca muralis; (4) conidia from Lappa major, 
Plantago major, Pulmonaria officinalis and Verbascum thapsiforme 
failed to infect any host inoculated. 
Salmon (128) reports the successful infection of Plantago major 
and P. media, using conidia from the former; negative results were 
obtained with Plantago lanceolata, Eupatorium cannabinum and 
Galium A parine. 
The writer (115, 116) has carried on a very extensive series of 
experiments with this mildew, particularly with the cucurbit hosts. 
In the main, the mildew as found on the Hubbard squash (Cucurbita 
maxima) was used for inoculating the various plants. It was found 
that this mildew readily infected Cucurbita maxima (seven varieties), 
C. moschata (three varieties), C. pepo (seventeen varieties), C. foeti- 
dissima, Cucumis dipsaceus, C. melo (nine varieties), C. sativus (eight 
varieties), Cyclanthera explodens, Echinocystis lobata, Lagenaria vulgaris 
(six varieties), Momordica charantia and Sicyos angulatus. Partial 
infection of the following was obtained: Cuitrullus vulgaris (seven 
varieties), Cucumis anguria (two varieties), Ecballium elaterium, 
Melothria scabra and Momordica balsamina. Coccinea cordifolia, 
Luffa acutangula and L. Aegyptiaca proved to be entirely resistant. 
To a slight extent it was possible to transfer the cucurbit mildew to 
the sunflower (Helianthus annuus) and plantain (Plantago rugellii). 
Efforts to transfer it to Aster cordifolius, A. laevis and Solidago caesia 
failed. It was also found that a race of mildew occurred on Aster 
cordifolius, A. laevis and A. sagittifolius, not passing over to Cucurbita 
maxima nor Solidago caesia. Another race occurs on Solidago caesia, 
infecting this species but not passing over to asters or cucurbits. 
Erysiphe graminis DC. Marchal (97) was the first to demonstrate 
host specialization in this powdery mildew. As a result of his tests he 
concluded that the following races may be distinguished, although he 
gives us no details of his evidence: 
1. Tritict upon Triticum vulgare, T. Spelta, T. polonicum and T. 
turgidum; not on T. durum, T. monococcum nor T. dicoccum. 
2. Hordei upon Hordeum hexastichon, H. vulgare, H. trifurcatum, H. 
nudum, H. jubatum and H. murinum; not on H. maritimum, 
H. secalinum nor H. bulbosum. 
3. Secalis upon Secale cereale and S. anatolicum. 
4. Avenae upon Avena sativa, A. fatua, A. orientalis and Arrhenatherum 
elatius. 
26 
