MILDEWS, RUSTS AND SMUTS 49 
20 — 23 X 10—13 [ 1 , rarely produced on the living host- 
plant. 
Parasitic on the leaves of various grasses, as species of 
Agropyron, Agrostis, Hordeiim, Phleum, Poa, Festiica, etc. 
Erysiphe tortilis, Fries. Mycelium thin, effused, soon 
disappearing, mostly on the under surface of the leaf; 
perithecia very much crowded as a rule, sometimes scattered, 
65—no p diam. ; appendages very long, 10—20 times as 
long as the diameter of the perithecium, 8—20 or more in 
number, wavy, brown, becoming more or less erect and form¬ 
ing a tuft, weak ; asci 2—5, usually 4 ; spores 4—8, usually 
8, 20—24 X 10—14 [1. 
Readily distinguished by the long, weak, wavy appen¬ 
dages, which form a tuft over the perithecium. 
Parasitic on the leaves of Cornus sanguinea and other 
species of Cornus. 
Erysiphe polygoni, D.C. Mycelium variable, thin and 
effused, or forming dense patches; perithecia usually 
scattered, rarely crowded, 65—180 p, usually about 90 p 
diam. ; appendages very variable in number and length, 
always spreading horizontally, often interwoven with the 
mycelium ; asci usually few, 2—8 ; spores 3—8, very 
rarely only 2, 19—25 X 9—14 p. 
Syn. Erysiphe trifolii, Grev. 
Erysiphe communis, Grev. 
Erysiphe martii, Lev. 
Parasitic on plants belonging to many different orders, 
as Achillea, Pisum, Vida, Capsella, Asperula, Circaea, 
Convolvulus, Delphinium, etc. 
Often destructive to cultivated peas, beans, tares, etc. 
PERISPORIACEAE 
This family is allied to the Erysiphaceae, differing 
principally in having dark coloured or black mycelium, 
perithecia, and coloured spores, which are often more than 
I-celled. Conidial stages are often present, but never of 
the oidium form, so characteristic of the Erysiphaceae. 
The family is essentially extra-European, and highly charac¬ 
teristic of tropical countries, where leaves more or less 
covered with jet-black, velvety patches, are quite as abun¬ 
dant as foliage covered with the snow-white oidium stage 
of the Erysiphaceae is in this country. There are but very 
few representatives of this family in Europe, and in this 
country the one representative of the genus Thielavia is 
E 
