226 CULTURE OF THE GRAPE. 



ruptured the pores, that, so to speak, the ground is 

 broken up, and prepared for the fungus-seed to take 

 root. Strong currents of wind, and exposure to clear 

 sun by. day and cold dews at night, have each a ten- 

 dency to disorganize the delicate leaf-tissue. Possibly 

 it may be, that, when active respiration is going on 

 from the leaves during dry weather, this respiration is 

 suddenly checked when damp weather comes on, and 

 the leaves may become gorged with sap, which cannot 

 pass off by evaporation; and, as a consequence,, the 

 tissue becomes disorganized. 



Mr. J. N. Jones, of Charleston, S.C., communicates to 

 "The Gardener's Monthly" (vol. ii. p. 363) the result of 

 his observations upon mildew, under the microscope, 

 which confirm this view. He says, " I had always con- 

 sidered mildew as a disease of plants, or at least as a 

 cause of disease, regarding it as a parasitic fungus, feed- 

 ing upon the sap, obstructing the respiration^ and destrovr 

 ing the vegetable tissue. I observed, however, that be- 

 fore the fungus made its appearance, and. before any 

 trace of it could be observed under a high magnifying 

 power, the foliage in parts, and sometimes entire leaves, 

 put on a peculiar glazed appearance, evidently caused by 

 the exudation of some gummy or viscid matter oozing 



