Ever since Franklin's great experiment, gypsum or sulphate of lime has generally been considered as possessing much fertilising power, and of being of great importance in agriculture. Having paid some attention to this substance, I make known my results, in the hope that they may be found of value to the public.

1. I filled two zinc boxes with pure sulphate of lime obtained from the double decomposition of sulphate of soda and chloride of calcium; in one of these boxes I sowed some grass seeds, in the other some wheat. The two boxes were then placed under glass shades, in order that all external influences might be avoided: the seeds were watered every other day. At the end of a few weeks plants had come up green and healthy, as in common soil; but as they developed, their fine appearance diminished, and at the end of a fortnight they looked dried and withered.

2. In boxes similar to the first, I placed a mixture of equal quantities of pure sulphate of lime, obtained as before, and clay, and sowed the same seeds as in the last experiment; the plants came up, but not nearly so well as in an unartificial soil, and they did not ripen.

3. In boxes, and under circumstances the same as before, I sowed the same seeds on dung covered over with a layer of sulphate of lime three-tenths of an inch deep. At the end of a fortnight the plants had come up and grown wonderfully; they ripened well and were magnificent specimens.

These facts, though of considerable practical importance, would not have shown in what way sulphate of lime really acts, had it not been for the following accident:

Happening to have a glass of muriatic acid in my hand one day, when looking at box No. 3,I accidentally spilled some of the acid on one of the boxes, and to my great surprise the lime effervesced, and on further examination I was satisfied that the sulphate had become changed into carbonate of lime. I concluded from this fact that the carbonate of ammonia, given off by the decomposition of the dung, being volatalised by the heat of the sun, came in contact with the sulphate of lime, when double decomposition ensued.

To ascertain how far this was true, I got some zinc pots, with bottoms pierced like a sieve; in the pots I placed some dung, then some sulphate of lime, and then I sowed some grass seeds.

When the plants had appeared and become tolerably developed, I watered them abundantly for a quarter of an hour, and in the liquid which flowed from the bottom of the pots I found sulphate of ammonia, whilst on the surface of the pots there was evidently carbonate of lime. This confirmed the view I had adopted.

I then made other experiments, which do not, however, bear upon the last mentioned facts. For example, I watered grass seeds sown in manure, in pots with pierced bottoms, with water containing one of the following substances, viz: sulphuric acid, muriatic acid, nitric acid, acetic acid, sulphate of iron, sulphate of potash, chloride of manganese, phosphate of soda, sulphate of magnesia, nitrate of soda.

With all these substances the grass grew well, and from the bottoms of the pots I obtained salts of ammonia, which are not volatile at the ordinary temperature. From all these facts I think we may conclude 1. That gypsum has by itself no fertilising power, and is alone useless as a manure.

2. That gypsum only is useful in agriculture when mixed with substances containing ammonia; in which case there is a double decomposition, and the ammonia is stored up for the use of the plants.

3. That for gypsum may be substituted any other salt which will fix ammonia, and render it not volatile at the ordinary temperature.

It is my intention next year to repeat these experiments on a large scale, in order to ascertain their real practical value. - Comptes Rendas. --------Method of Preserving young Fruit-Trees from the attacks of Hares and Rabbits.- All lovers of gardens know by experience that hares and rabbits devour with great avidity the annual bark of young fruit trees, and particularly of dwarf apple trees, among which the most healthy and vigorous are always destroyed the first, in consequence of their bark being the most tender and savoury. As soon as the ground is covered with snow,these animals, no longer finding anything in the fields on which they can browse, begin their devastations in the gardens: if they are numerous, and the fall of snow heavy, a few nights only are sufficient for them completely to ruin the most beautiful plantation, and to annihilate the result of many years of labor and care. Happily, nothing is more easy than to place these trees beyond the attacks of these marauders protected by the law. The following is the plan I have adopted with complete success during the last six or seven years. I mix about 4 1/2 pounds of quick-lime, in lumps, with 2 1/2 gallons of water, and add a few handfuls of soot, stirring the liquid until the two substances are intimately incorporated.

I then take a handful of Rye-straw and bind it on a stick to form a kind of brush, with which I grey-wash the trunk and branches of my trees from the ground to at least a yard above it; for should the snow drift by the wind against the foot of the trees, the hares, by means of the inclined plane thus afforded them, would be able to attack the trees at a much greater height. The wash, applied hot, has also the advantage of preserving the bark of the trees in a state of perfect health, and preventing the increase of moss, which is often pernicious in its effect, and always very disagreeable to the eye. It is desirable that this preservative application should be made in dry weather, in order that the mixture on drying may adhere to the bark; for should it rain at the time, or immediately afterwards, the mixture would be washed from the trees, and it would be necessary to re-commence the operation. If the mixture also is applied during a frost, there would be little chance of perfect success; as the Dart of the bark on which it would be laid would be thawed.

If, however, through want of foresight, a frost sets in during the course of the operation, and it becomes urgent to complete it, we may do so with perfect success by choosing that moment of the day in which the sun strikes most strongly with his rays the trees on which we wish to operate. Three gallons of this wash are sufficient to secure two or three hundred dwarf trees from the ravages of hares; a result that may be obtained for a pennyworth of lime and the day's work of an active laborer. This plan is equally infallible for the preservation of grafts and all nursery collections. From the French of the Baron Vander-Streeten (in the Jour-nal Agricole de Verviers.)