(55) 
zoospores which appear identical with those produced by the conidia. The 
office of the oospore appears to be to pass the winter. The family consists 
of two genera, Feronospora and Cystopus. The species of the former have 
the appearance of moulds, producing conidia singly or in clusters at the 
tips of the fertile threads, while those of the latter occur as white pustules 
on leaves, bearing the conidia in moniliform strings, the fertile hyphae or 
threads having no prominence. Generally the mycelium of both has curious 
processes, termed kauptoria, penetrating the cells of the supporting plant, 
as shown in Plate II, Fig 7. The threads themselves, when first emitted 
from the spore as well as when buried and ramified in the tissues, often pen- 
etrate the cell through and through, being found at considerable distances 
from the diseased-looking spots upon which the fruiting threads appear. 
Over forty species of Feronospora have been described, of which only 
six are known to exist in the United States. Many others probably await 
the researches of botanists. Of the six, three, by far the most common 
ones, are in the present described collection. 
Feronospora in/estans, Mont., ( Plate II, Fig. 8.) Very common on 
potatoes and tomatoes. It has also been found on Bittersweet ( Solanum 
dulcamara ), and even upon a not closely related plant, Anthoceris viscosa (12) 
belonging to the Scrophulariaceae. This is by far the most famous, or in- 
famous, of the species of this genus, causing the well known and often 
dreaded potato rot. Its history has been often told (13), but a new chapter 
was added last year by Worthington G. Smith (14), of England. Previously 
the oospores had not been found as such, and so much search had been 
made for them that it was quite generally believed that they must exist 
upon some other supporting plant. Clover, among others, was suspected. 
The finding of them in the tissues of the leaves and stalks of the potato 
settled the doubt and bids growers beware of leaving the old potato top to 
breed the pestilence another year. 
F. gangliformis. Berk, ( Plate II, Fig. 3.) Common on lettuce and 
some allied composite ( Lactuca altissima and Nabalus albus. Farlow.') 
Zoospores not observed. Conidia germinating and penetrating young 
leaves, the tissues usually decaying from above downward until the whole 
plant is involved and becomes a slushy, putrescent mass. This parasite is 
especially destructive in forcing-houses. Several hundred dollars worth of 
lettuce was lost by one propagator here last winter from this fungus (15). 
The only cure now known is to keep the atmosphere as dry as practicable 
and remove very carefully the diseased leaves. 
P. viticola , B. & C. ( Plate II., Figs. 6 & 7.) Common on grape 
leaves, and becoming very destructive in this vicinity, worse apparently 
12. Farlow, Synopsis of the Peronosporeae of the United States, Bulletin of 
the Bussey Institution, p. 426. 
13. Smith, Ohio A g. Report, 1872, Essays, etc., p. 20. 
14. Farlow, Gardener’s Monthly, Nov. 1875, p. 274. Smith, Ohio A g. Report, 
1862, Essays, etc., p 20. 
15. Smith, Gardener’s Chronicle, July 17, 1875, p. 69. Quarterly Journal of 
Microscopic Science, October, 1875. 
16. Farlow on the American Grape Vine Disease. Bulletin Bussey Institution, 
p. 415. 
