174 MICROSCOPIC ITJNGI. 



variety found on the alder is given in the plate XI. 

 fig. 234. 



We have found another species which had not 

 been before noticed in this country {M. Hedwigii, 

 Lev.), on the leaves of the mealy guelder-rose in the 

 vicinity of Darenth Wood, near Dartford, in Kent. 

 The mealy character of the leaves of this plant, and 

 the minute size of the conceptacles of the parasite, 

 render it difficult to find ; indeed, it could not be 

 noticed unless it were sought for, as we sought it, 

 lens in hand. It only occurs on the under surface 

 of the leaves : the mycelium is very web-hke and 

 fugacious, the conceptacles minute, globose, and 

 scattered (fig. 243). Four sporangia, each contain- 

 ing but four spores (fig. 244), are enclosed in each 

 conceptacle, which is surrounded by a few append- 

 ages (about six) thrice dichotomous, and thickened 

 at the tips of the ultimate branches, which are 

 incurved (fig. 247). 



The species of true Erysiphe are distinguished 

 botanically from the foregoing by the floccose 

 character of the appendages, in which feature they 

 accord with the species found on the rose and the 

 hop, but from which they differ in the conceptacles 

 containing numerous sporangia instead of only one, 

 as in those species. 



One of the most common and conspicuous of these 

 is foimd on the leaves and leaf-like stipules of the 

 garden pea. Every leaf in a crop will sometimes 

 suffer, and the gardener, to his great mortification. 



