76 DISTEMPERS OF CORN. Part I. 



clammy dews which fome of our authors mention, as falHng in 

 clofe weather, flopping the perfpiration of plants, and hindering the 

 fap from afcending to nourilh the flowers, &c. 



Mr. Tillet, in fupport of his opinion, quotes a memoir of Mr. 

 Reneaume, publiflied in theTranfadlions of the Academy of Sciences, 

 on the extravafation of the nutritive juice of Walnut-trees in 

 Dauphiny; of the manna of Calabria, which is not a dew, but the 

 extravafated juice of the leaves of a kind of afli j and what M. 

 Mufchenbroeck relates in his Phyfical Eflays, of thick and oily 

 juices, which iffues out at the excretory vefTels of leaves, and ftop 

 there in the confiflence of honey. 



Mr. Tillet, from feveral fa<5ts which he mentions, concludes that 

 the rujl or mealy powder which is obferved on many plants, is not a 

 coUedlion of the eggs of infecSts ; but that it depends on the quality 

 of the juices of particular plants, when the thinner parts are evapo- 

 rated. Thus, it is red on garden beans, of a rufty colour on all 

 kinds of corn, greenilh on the plum, yellowifh on the afh, white 

 on larch trees, 6cc. 



M. Duhamel tried frequently to produce the fame effedls which 

 the dry weather occafions, by applying to the leaves of many plants, 

 acid and corrofive liquors, to others alkahne and fpirituous liquors, 

 and frequently fuch clammy glutinous fubftances as might ftop the 

 perfpiration, without hurting the texture of the plants. Thefe trials 

 have not produced any thing like ruft. But who can tell how far 

 experiments may lead philofophers ? Some little circumftance may 

 have efcaped us, which, obferved, might have led us near the objedt 

 of our fearch. The public welfare calls on all attentive obfervers; 

 to exert themfelves on fo ufeful a fubjedl. 



Mr. Worlidge's opinion of mildeius, which he holds to be quite 

 difi-'erent things from hUghts, is, that they are " caufed from the 

 *' condenfation of a fat and moift exhalation in a hot dry fummer; 

 *• from the blofToms and other parts of vegetables, and alfo from 

 " the earth itfelf, which, by the coolnefs and ferenity of the air in 

 " the night, or in the upper ferene region of the air, is condenfed 

 " into a fat glutinous matter, and falls to the earth again ; part 

 " whereof refls on the leaves of the oak, and fome other trees 

 " whofe leaves are fmooth, and do not eafily admit the moifture 

 " into them, as the elm or other rougher leaves do ; which mildew 

 " becomes the principal food of the induftrious bees, being of itfelf 

 " fweet, and eafily convertible into honey. 



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