THE HONEY DEW* 
43 
Aphis tilicB, He collected it from numerous indi- 
viduals wtiicli voided it wliilst on the wing. They 
rained it on glass plates placed to receive it^ and the 
deposit was analysed afterwards by Professor Gunning, 
of Amsterdam, who stated that, very unexpectedly, it 
principally consisted of cane sugar, and not of grape 
sugar or glucose. 
Boussingault* finally answered that he could prove 
that the fresh . lime leaves contained cane sugar, al- 
though less richly than can be shown by the diseased 
leaves. As also the secretion he examined contained 
both glucose and dextrine, it could not be, he conceived, 
the produce of Aphides. 
In another paper Boussingault describes a kind of 
manna which he obtained from the berries of the 
Service tree, but he does not connect this notice with 
the asserted vegetable origin of the honey dew. 
I am very much of the opinion that this honey dew, 
as found upon leaves, is of Aphis origin. The evidence 
of the polari scope, without an appeal to a sound 
chemical analysis, is not, I conceive, sufficiently strong 
to decide definitely against such an origin. Besides 
all this, the presence of dextrine need create no 
serious difficulty, since it is well known that saliva 
and biliary products, such as Aphides may be capable 
of secreting, produce dextrine by their action on 
starch. 
Future inquiry will clear up the question whether 
this liquid is identical with that discharged from the 
cornicles, and which, in some full-fed insects, even 
■exudes from the pores disposed down each side of the 
dorsum. Often this transpiration may be seen in 
Aphis cinerarim, of which I give a figure, but such an 
exudation is by no means confined to this species. 
It will be borne in mind that the siphuncles of 
Aphides are often styled nectaries, from the general 
belief that they emit the sweet liquid in question. 
As an appendix to the above remarks I may add a 
■ * Boussingault, same vol. p. 473 ; also tom. 74, p. 939. 
