We give place to the following from a correspondent of the London Garden, in order to call attention to a question we regard as by no means settled :

"Bee-keepers will rejoice greatly at what they regard as honey-dew, the deposit of which is very heavy this year, as aphis are more than usually prevalent, the undersides of the leaves of limes, sycamores, cherries, and most other trees, being quite covered with them, and, as a natural consequence, the foliage below is heavily coated with their excreta, which they exude in such quantity as to form a glutinous paste, and varnish the leaves quite over. Many look on this so-called honey-dew as a sort of distilled sweetness brought about by atmospheric influence, and never dream of aphis, or think it is the discharge from any insect, else they would not be found, as I have seen them, licking the nectar off, and appearing to enjoy it, till they knew from what source it came, when they soon showed disgust, and a violent fit of expectorating seized them. Hop-growers, and those connected with gardening, know only too well what hone\-dew means, and when they see it are well aware that the enemy is at work sucking the vital energies out of the plants, and crippling their growth.

What is wanted now is a good downpour of rain to wash the foliage, and cleanse it of both parasites and honey-dew; for though the latter may be good for the bees, and go far towards assisting them to fill their hives with honey, it stops the pores of the leaves, and prevents free respiration, and thus interferes with their health."

Now many of us have seen honeyed liquid excreted from aphides, and are therefore quite ready to agree with the notion of the animal origin of honey-dew as generally accepted.

But the writer is quite sure he has seen numbers of cases where trees have swarmed with aphides without any honeyed surface to the leaves below them, and on the other hand some few cases, especially on the linden, where no trace of any aphides existed. Only last season he saw the whole brick pavement beneath the shade of two American plane trees in front of the Wills Hospital in Philadelphia, covered with stains from drops of liquid which had fallen from the trees. Myriads of flies were feasting on the sweetness wasted there. So far as the eye could tell at that distance from the ground, no aphides were visible. By the aid of a sun umbrella handle, some of the lower leaves were gathered, but there were neither aphides beneath or any appearance of varnish on the upper surface of these shaded leaves. Across the street were other plane trees, the branches almost reaching those on the other side, but no sweet liquid was under these as in the other case. It is inconceivable that trees so near together should swarm with aphides in one case, and have none in the other.

These street trees were left with regret that they were not growing nearer where some close attention might be given towards unraveling the mys-tery. It seems, however, inconceivable that even though aphides should have been in extraordinary numbers on the tops of these trees, they should be able to excrete enough honey, not only to cover the myriads of leaves with a gloss below them, but have still some to spare to splash the brick sidewalk as with a hose. Though we have to give some sort of an assent to the aphid origin of honey-dew, we cannot help feeling there is something back of it all not yet explained. - Ed. G. M.