THE SMALLER FUNGI. 625 
be different forms of fruit produced by the same plant, 7. e., 
an instance of dimorphism.” 
A similar instance of this two-formed condition of the 
smaller fungi can be traced in the delicate mouldiness which 
covers the leaves of many plants, as the lilac, the grape, and 
the fruit of the gooseberry, and looks like strings of beads 
made of colorless cells, in this condition known or described 
as Oidium (Fig. 1; a, tuft of conidia of Fig. 1. 
O. monilioides X 120; b, portion of 
grass-leaf with the same species of blight. 
From Cooke), the spores being the self- 
same beads, and egg-shaped or oviform, 
whence the generic name ; but careful ob- 
servation will persuade us that this is 
hot the perfect condition ; and when later 
in autumn these threads become more 
compact, and are surmounted on their 
horizontal surfaces by shining black capsules, or perithecia, 
each of which is filled with elegant elliptical and elongated 
cells, and each in turn containing several spores, shall we 
find in Erisyphe that we have arrived at the conclusion of 
the dimorphism of this fungus, a parasite and injurious in its 
effects. The famous grape mildew, so destructive to the 
foliage of the wine and table grapes of Europe, and knows 
as Oidium Tuckert, is thus only an imperfect form of some 
common Hrisyphe, or mildew ; and in this portion of Massa- 
_ chusetts, so far as I have observed, it is the Uncinula spiralis 
(B. and C.) which attacked the foliage of the sweet wa 
grapes, as on vines of Mr. E. S. Rogers of Salem, m 1850, 
and the same ‘parasitic fungus which covered the leaves of 
the wild grape, Isabella, and other hardy varieties, and which 
can be detected every season to a greater or less extent. 
And besides this dimorphism thus apparent in the smaller 
fungi, stranger facts connected with their natural history 
Meet us here. Observation has detected in the Æcidium, or 
cluster-cups, not a perfect fungus as it would seem, but in 
79 
AMER. NATURALIST, VOL. I. ; 

