108 
placing them in water on a glass slide, under a bell jar. The conidia 
used for the purpose were taken from fresh leaves which had been 
gathered in the tin collecting box and had remained there several 
hours. They were placed in water during the day, and on the following 
morning they had thrown out their germ tubes. These show one or 
more peculiar swellings or bulb-like expansions. This is not rare in 
the Peronosporacem, but has been observed in a number of species. 
De Bary figures* the germinating conidia of F. cffusa and several other 
species showing this character. 
There is often more than one conidiophore extending from a stoma. 
In some cases as many as five were seen. (Plate xvii, Fig. 10.) The 
manner in which the conidia originate from the mycelium is the same as 
in Bremia lactucw as figured by Cornu, t A mycelial thread running 
near a stoma sends out a branch which is contracted at the point of emis¬ 
sion, but soon swells out so as to nearly equal the parent branch. As it 
nears the opening of the stoma it narrows down to a small filament 
which passes through the opening between the guard cells and then 
swells out into the bulb-like base of the conidiophore. 
Type specimens of both these species have been deposited in the her¬ 
barium of the Division of Vegetable Pathology, U. S. Department of 
Agriculture, and have been sent to the following herbaria: Philadelphia 
Academy of Science; Columbia College, New York; Harvard University, 
Cambridge, Mass.; Boyal Herbarium, Kew, England; Museum of Natu¬ 
ral History, Paris; Boyal Botanic Garden, Berlin; Boyal Botanic Gar¬ 
den, Borne; Museum of the Boyal Botanic Garden, St. Petersburg, and 
to several individuals. 
EXPLANATION OF PLATE XVII. 
Figs. 1-16, Peronospora celtidis, n. sp. 
Figs. 
1,2. Leaves of Celtis occiclentalis showing spots caused by the Peronospora. 
3. Typical conidiophore X 224. The branches do not all lie in one plane, 
as the figure might lead one to think, but are arranged around the 
stem like the branches of a tree. The lowest branch extends to the 
right and upward; the second branch extends to the left and also 
slightly upward. 
4. Conidiophore below the average size, X 224. 
5. Tips of the conidiophore more enlarged, X 640. 
6. Young conidiophore with conidia attached, X 224. 
7. Conidiophore nearly mature but with protoplasm still in the stem, X 
224. 
8. Conidium, with its contained zoospores, just ready to burst. 
9. Conidium discharging its zoospores. 
*Reclierches sur le ddveloppment de quelques Champignons Parasites. Ann. Sci. 
Nat. Botanique, sdr. 4 C tome xx, Plate 8, Fig. 7. 
t Institute de France. Acaddmie des Sciences. Observations sur le Phylloxera 
et sur les Parasitaires de la Vigne, etc. Ltudes sur les Peronospordes. I. Le Meu- 
nier, Maladie des Laitues, 1881. 
