6 
KOYAL HORTICULTURAL SOCIETY. 
some other trees. " We cannot affirm," he says, " either that they 
are a natural excretion, or that they are produced by insects " 
{I.C.J p. 240). Dr. Masters states in the Treasury of Botany 
(p. 38) that a manna-like substance is produced from species of 
Alhagi, and that it is an exudation from the leaves and branches of 
the plant only appearing in hot weather. Saline secretions from 
leaves have been more frequently observed. De Saussure states 
that an accumulation of saline matters at their surface often occurs 
in garden vegetables ; transpiration being impeded, the leaves are 
ultimately destroyed {Recherches, 264, 265). De CandoUe found a 
saline secretion from the leaves of a Eeaumuria to consist of 
carbonates of soda and potash*' {Fhya. Veg. i., 237). — W. T. D.] 
[Note read May 1.] 
My attention has been drawn by Dr. Masters to two papers in 
the EuU. de la Soc. Bot. de Fr. for 1867, which advance a view of 
the origin of honey-dew quite different to that held by Boussingault. 
The method of investigation was exactly similar ; the leaves were 
washed, and the mode of accumulation of the honey-dew subse- 
quently was described in almost the same words. It is attributed, 
however, not to an exudation from the plants, but to the excretions 
of parasitic insects which were to be found on the foliage above 
that on which the honey-dew made its appearance. The insects, it 
is stated, have the power of projecting their excretions a distance of 
4 — 5 inches, and it is thought that the action of the wind would 
convey them even further. Eiviere appears to have been the first 
to observe this curious habit, and to have been confirmed by other 
entomologists. After the honey-dew had attained a thickened con- 
sistence it became the seat of growth of various microscopic Tungi, 
referred to the genus Fumago [but subsequently distributed amongst 
Capnodiu7n, CladosporiunifSLTid. Antennaria (see ''Journal of the Eoyal 
Horticultural Society," 1849, pp. 243—260)], giving the plant a 
blackened appearance. The invasion by a host of aphides of two 
Lime-trees resulted in the blackening of a terrace which they over- 
shadowed, and of the seats placed upon it. In the case observed 
by Boussingault it is difficult to think that so careful an observer 
would not have satisfied himself thoroughly of the absence of 
* Mr. Douglas, of Loxford Hall Gardens, Ilford, stated after the meeting 
that he has some Orange-trees at the back of a Cucumber-house which are 
frequently afifected -with honey-dew, though no green-fly ever gets near them, 
and that he has long been perfectly satisfied that honey-dew is not the result 
of insect agency. 
