"Under this general name, I purpose to include the consideration of gumming, bleeding, and other injurious affections under which plants occasionally labour, on account of their sap escaping from the properly containing vessels. The extravasation proceeds either from the alburnum or from the inner bark and may arise from five causes.

"1. The acrid or alkaline state of the sap, which has been considered already, when treating of the canker.

"2. From plethora or excessive abundance of the sap.

"3. From the unnatural contraction of the circulatory vessels.

"4. From wounds.

"5. Heat and dryness.

"1. With regard to the alkaline state of the sap, it may be observed, additionally, that the excessive alkaline quality of the sap, imparting to it the power of destroying the fibre of its containing vessels, is placed on the basis of chemical experiment. A weak alkaline solution dissolves woody fibre without alteration; and it may be thrown down again by means of an acid. By this property we are enabled to separate wood from most of the other vegetable principles, as few of them are soluble in weak alkaline leys.

"It is true, that the vital principle may counteract powerfully this chemical action; but it will not control the corrosive effect of an active agent in excess, if repeated for any length of time. The blood of the human system contains, when in a healthy state, a portion of common salt; yet, if this saline constituent is in excess, it induces inflammation and organic derangement.

"2. Plethora is that state of a plant's excessive vigour in which the sap is formed more rapidly than the circulatory vessels can convey it away. When this occurs, rupture must take place, for the force with which it is propelled during circulation, and consequently, the force acting to burst the vessels during any check, is very much greater than could have been expected, before Mr. Hales demonstrated it by experiment.

"Now, we know that a much less pressure than any of those above mentioned would be capable of bursting the delicate membranes of any of their exterior descending sap vessels, and it is in such outer ducts that the injury first occurs. When one exterior vessel is ruptured, that next beneath it, having the supporting pressure removed, is enabled to follow the same course at the same locality; and in proportion to the length of the time that the sap continues in excess, is the depth to which the mischief extends, and the quantity of sap extravasated.

"If the extravasation proceeds from this cause, there is but one course of treatment to be pursued; sever one of the main roots to afford the tree immediate relief, and reduce the staple of the soil, by removing some of it, and admixing less fertile earthy components, as sand or chalk. This must be done gradually, for the fibrous roots that are suited for the collection of food from a fertile soil are not at once adapted for the introsusception of that from a less abundant pasturage. Care must be taken not to apply the above remedies before it is clearly ascertained that the cause is not an unnatural contraction of the sap vessels, because, in such case, the treatment might be injurious rather blood from the human frame, as a relief to the system.

"4. The extravasation of the sap from a wound is usually the most exhausting, and as the wound, whether contused or not, is liable to be a lodgment for water and other foreign bodies opposed to the healing of the injured part, the discharge is often protracted. This is especially the case if the wound be made in the spring, before the leaves are developed, as in performing the winter pruning of the vine later than is proper. In such case, the vine always is weakened, and in some instances it has been destroyed. The quantity of sap which may be made to flow from some trees is astonishing, especially in tropical climates. Thus, from a cocoa-nut palm, from three to five pints of sap will flow during every day for four or five successive weeks. The best mode of checking such exudations, is by placing a piece of sponge dipped in a solution of sulphate of iron upon the discharging place, covering the sponge with a piece of sheet-lead, and binding it on firmly. The sulphate acts as a styptic, promoting the contraction of the mouths of the vessels; the sponge encourages cicatrization, and the lead excludes moisture.

"5. Heat attended by dryness of the soil, as during the drought of summer, is very liable to produce an unnatural "The honey-dew was noticed by the ancients, and is mentioned by Pliny by the fanciful designation of the 'sweat of the heavens,' and the 'saliva of the stars,' though he questioned whether it is a deposition from the air, purging it from some contracted impurity. More modern philosophers have been quite as erroneous and discordant in their opinion relative to the disease's nature. Some, with the most unmitigable aspe- rity, declare that it is the excrement of aphides. Others as exclusively maintain that it is an atmospheric deposit, and a third party consider that it arises from bleeding, consequent to the wounds of insects. That there may be a glutinous saccharine liquid found upon the leaves of plants arising from the first and third named causes is probable, or rather certain; but this is by no means conclusive that there is not a similar liquid extravasated upon the surface of the leaves, owing to some unhealthy action of their vessels. It is with this description of honey-dew that we are here concerned.

The error into which writers on this subject appear to have fallen, consists in their having endeavoured to assign the origin of every kind of honey-dew to the same cause. Thus the Rev. Gilbert White seems (Naturalist's Calendar, 144) to have had a fanciful and comprehensive mode of accounting for the origin of honey-dew: he tells us, June 4th, 1783, vast honey-dews this week. The reason of this seems to be, that in hot days the effluvia of flowers are drawn up by a brisk evaporation, and then in the night fall down with the dews with which they are entangled. The objection urged to this theory by Curtis (Trans. Linn. Soc. vi. 82) is conclusive. If it fell from the atmosphere, it would cover every thing on which it fell indiscriminately; whereas we never find it, but on certain living plants and trees; we find it also on plants in stoves and green-houses with covered glass.

"Curtis had convinced himself that the honey-dew was merely the excrement of the aphides, and he supported his theory with his usual ability, although he justly deemed it a little 'wonderful extraordinary' that any insect should secrete as excrementitious matter, sugar; he even thought it possible, if the ants, wasps, and flies, could be prevented from devouring the honeydew, 'almost as fast as it was deposited,' to collect it in considerable quantities, and convert it into the choicest sugar and sugar-candy.'

"The bees, however, he found totally disregarded the honey-dew which came under his observation. With the opinion of Mr. Curtis I do not agree, any more than does the Abbe Boissier de Sauvages, who, in a memoir read before the Society of Sciences at Mont-pellier, gives an account of 'a shower of honey-dew,' which he witnessed under a lime tree in the king's garden at Paris.

"The various successful applications of liquids to plants, in order to prevent the occurrence of the honey-dew and similar diseases, would seem to indicate that a morbid state of the sap is the chief cause of the honey-dew, for otherwise it would be difficult to explain the reason why the use of a solution of common salt in water applied to the soil in which a plant is growing, can prevent a disease caused by insects. But if we admit that the irregular action of the sap is the cause of the disorder, then we can understand that a portion of salt introduced in the juices of the plant would naturally have a tendency to correct or vary any morbid tendency, either correcting the too rapid secretion of sap, stimulating it in promoting its regular formation, or preserving its fluidity. And that by such a treatment the honey-dew may be entirely prevented, I have myself often witnessed in my own garden, when experimentalizing with totally different objects. Thus I have seen plants of various kinds, which have been treated with a weak solution of common salt and water, totally escape the honey-dew, where trees of the same kind growing in the same plot of ground not so treated, have been materially injured by its ravages.

I think, however, that the solution which has been sometimes employed for this purpose is much too strong for watering plants. I have always preferred a weak liquid, and I am of opinion, that one ounce of salt (chloride of sodium) to a gallon of water is quite powerful enough for the intended purpose. I am in doubt as to the correctness of Knight's opinion, as to the mere water having any material influence in the composition of such a remedy, since I have noticed that standard fruit trees, around which, at a distance of six or eight feet from the stem, I had deposited at a depth of twelve inches a quantity of salt to promote the general health and fruitfulness of the tree, according to the manner formerly adopted to some extent in the cider countries for the apple orchards, that these escaped the honey-dew which infected adjacent trees, just as well as those which had been watered with salt and water." - Johnson's Principles of Gardening.