86 AUSTRALASIAN 
and is sweet like honey ;” while some assert that it is the 
secretion of aphides, or plant lice ; and others, that it is simply 
an exudation from the plants or trees on which it is found. 
The first-mentioned idea is now quite exploded ; the two latter, 
between them, contain the truth. German apiarists make a 
distinction between Honigthau (honey-dew), which they look on 
as an excretion of aphides, and Nebenblatihonig, which they 
consider to be exuded by the leaf-buds of certain plants or 
trees. Liebig asserts that when 
“the quantity of sugar present (in the sap of a tree) is greater 
than can be exhausted by the leaves and buds, it is execeted from the 
surface of the leaves or bark. Certain diseases of trees, for example 
that called honey-dew, evidently depend on the want of the due 
proportion between the quantity of azotised and that of the unazotised 
substances which are applied to them as nutriment. .... When a 
sufficient quantity of nitrogen is not present to aid in the assimilation 
of the substances destitute of it, these substances will be separated 
as excrements from the bark, roots, leaves, and branches. The exuda- 
tions of gum, mannite, and sugar, in strong and healthy plants, 
cannot be ascribed to any other cause.” 
He instances several cases of copious exudation of a thick 
sweet liquid from the leaves of trees, more especially from 
those of the linden, during a hot and dry summer. Ludwig 
Huber, in his Bienenzucht (1880), mentions three sorts of 
Homigthau, one which is voided by the plant lice, which is the 
worst; ‘it is tough, tasteless, and unhealthy for the bees in 
winter ;” another is obtained from the leaves of the oak, which, 
when bitten by a certain kind of beetle, give out, “ by favour- 
able temperature, a sweet liquid, which the bees eagerly lick 
up ;” and the third sort is exuded from the leaves of the linden, 
oak, plum, and other trees, generally in the early mornings, by 
a change of temperature after very close, hot weather. Most 
of the American writers on bee-keeping appear to have had 
little or no personal experience of honey-dew. Professor Cook 
mentions it as occurring in California, in a case where it was 
unmistakably exuded from the tree leaves; and Langstroth 
quotes the English entomologists, Spence and Kirby, as to clear 
cases of plant-louse origin ; also Bevan, who, however, does not 
suggest anything as to the cause of the phenomenon, but merely 
says :— 
‘* Honey-dew usually appears upon the leaves as a viscid transparent 
substance, as sweet as honey itself, sometimes in the form of globules, 
