CULTURE OF THE GRAPE. 225 



of the grapes and wine yielded by such soils, are mani- 

 fest proofs of the value of ashes. . . . Let every one 

 troubled with the mildew, especially in grapes, make a 

 fair trial of it, and report for the benefit of others. There 

 are certainly soils where this plant thrives wonderfully 

 well, and no mildew appears ; and others, where, with all 

 ordinary care, it can seldom be prevented. If the appli- 

 cation of potash in the form of wood-ashes will insure 

 the cultivator against mildew in grapes alone, it is a dis- 

 covery of no* ordinary utility." The form of expression 

 which is used by " Chemico," that " mildew is caused by 

 a surplus of carbonic-acid gas," is unfortunate. But 

 there is plausibility in the theory, that a superabundance 

 of carbonic-acid gas in wet weather may act upon leaves 

 having an insufficient supply of potassa, and thus cause a 

 diseased state which invites fungi. At any rate, we 

 know that potash will give that vigor which will en- 

 able the vine the better to resist mildew. 



Sudden changes from heat to cold, and from wet to 

 dry, are conditions which universally develop mildew; 

 but these are not conditions which specially favor, the 

 growth of the fungus plant. We must therefore con- 

 clude that these sudden fluctuations have so disar- 

 ranged the delicate tissues of the leaves, and perhaps 



15 



