105 
DESCRIPTION OF TWO NEW SPECIES OF PERONOSPORA. 
By M. B. Waite. 
PERONOSPORA CELTIDIS. 
(Plate XVII, Figs. 1-16.) 
Spots definite, angular, minute, about l mm or less in diameter, limited 
by tlie vein lets; by confluence forming irregular patches or covering 
the greater part of the leaf; dark purple above, and when close together 
surrounded by an indistinct yellow border; on the under side at first 
dark green in color, with a water-soaked appearance, becoming ashy 
gray as the conidiopliores are thrown np, then brownish, the confluent 
patches soon becoming brown. 
Mycelial liyplim small, delicate, much branched, from 3 to 7£// in di¬ 
ameter, averaging about G//, with very thin and hyaline cell walls. 
Haustoria not seen. 
Conidiopliores slender, four to five times branched and bearing from 14 
to 28 conidia, branching in the so-called dichotomous manner, but with 
the first branch extending outward at nearly a right angle. Branches 
and tips nearly straight, tips gradually tapering to a blunt point. Total 
length of the conidiopliores 200 to 320//. Length of the stem to the first 
branch nearly equal to the length of the head from the first branch to 
the tip. 
Conidia elliptical, nearly twice as long as broad, 14 by 26// to 20 by 38//, 
averaging about 1G by 31//, provided with a blunt apiculus and a 
swelling at the base which closely resembles that at the apex, making 
the two ends appear alike, dark, smoky colored; germinating by zo¬ 
ospores, eight or nine in number, which break through the apical jiapil- 
lus. In living specimens viewed with a low power of the microscope 
as an opaque object the conidia appear black, and the conidiopliores are 
hygroscopic. 
Oospores produced abundantly in the leaf parenchyma, to which the 
whole fungus seems to be limited ; subglobose, light brown in color, 28 
by 3G/t to 30 by 44//; endospore rather thin; exospore smooth, quite 
variable in thickness, causing the margin of the oospore to appear un¬ 
dulate in cross section. Walls of the oogonium thin. 
On Celtis occidentalism L. Washington, D. C., October 7, 1891, Herb. 
M. B. Waite, No. 55G; October 9, 1891, Herb. M. B. W., No. 557. 
Still Pond, Md., October 10,1891, Herb. W. T. Swingle, Nos. 402G, 4027. 
Observations: —This species is an exceptional form in many respects. 
It is the only species in the family so far found growingon a tree, although 
Phytophthora omnivora grows on seedlings of Fay us and other trees, and 
Plasmopara viburni, Peck, on Viburnum ; P. viticola, on Vitis; P. ribicola 
on kibes, Peronospora sparsa on Rosa and P. ruin on Rubus all grow on 
woody plants. The spots formed on the leaves are usually small and 
