328 



DISEASES 



Sect. XIV. i. 



/' 



tures ; 



hich were made fome weeks earlier In the year, and by 



without wni^s, and differing fonaewhat in their 



fli 



b 



any appearance of honey-dew on thofe 



But I could 



difcover any pundures or other difeafe of the leaves of thefe 



trees, 



d therefore doubt whether thefe infed 



th 



cr 



h fo 



1 the under furface of every leaf, could be the caufe of the mor- 

 bid exfudation, if fuch it was, on their upper furfaces ; and the more 



I 



Id 



diflingulfh, that they preyed 



upon the honey thus 

 produced ; and I afterwards obferved that they continued in immenfe 



mbers under every leaf, wh 



th 



e 



ther became cooler, and 



moifl 



I 



d the honey-dew 



fed to be vifibl 



But after a fe 



\ 



weeks I obferved the upper furface of every leaf became covered with 

 a black powder like foot ; whether this was a new material, or re- 

 mained after the exhalation of the honey-dew, I did not determine by 



■ 



experiment. But if both the honey-dew and this fubfequent black 

 powder on the upper furfaces of the leaves, were the excrement of 

 the aphis on the under furfaces of the leaves over the former, or ow- 

 ing to an exfudation from the tree, muil be determined by further 



jobfervatlons. 



But as a fecond period of fap-flow is believed to exift about mid 



fummer, or a depofition of vegetable nutriment for the new buds, a 



jre is reafon to fufped, that the ho 



^ 



defcribed in Se^t. Ill 



8. th 



ney-dew is owing to the inverted aclion of the exterr 

 ©ccafioned bv the debility induced by the continued b 



lymph 

 . and 



f fituation. Wh 



haps to the moiflure ( 



thrown upon the external habit inftead of being applied 



pe 

 the nutritive fluid 



to 



fh 



the new buds, or to be laid up as a refervoir for their ufe. And th 



if it be voided by the aph 



punduring the fap 



vefl'els with the fine probofcis, which they pofTefs, at this feafon only, 

 or in a diftempered ftate of the tree, and drinking more of it than 

 they are able to digefl:. For a further hiftory of this Infed fee No. 



^. 2,. of this Se(3;iQn. , , 



8. Exfudatio 



fl J 



