A valued correspondent, in a previous page, has given our readers a very interesting paper on Climate, a subject of the greatest importance to all of us. We would caution the farmer, no less than the horticulturist, not to estimate the value of his climate entirely by the quantity of rain that falls in a given district. Water, as the universal solvent of the nutritive matters, is indispensable, but much unnecessary trouble has been taken to calculate the quantity of water, as rain or snow, that falls upon the surface of the earth. The free water of the soil, many scientific men think, is seldom beneficial to plants, and only bog plants, or those which grow in water, will exist in it. In those portions of the earth which produce the most plants, water is only occasionally present (as after rain, etc.) as a coherent fluid; the normal condition of water in the soil is as hygroscopic water, or absorbed vapor. The complete independence in vegetation of the atmospheric precipitation of rain in a liquid form, is seen in the vegetation of the oasis, and of the cloudless coasts of Chili and Peru. The sand of Sahara produces no vegetation, not because no rain falls upon it, but because it has not the power of condensing aqueous vapor.

Of the water that falls as rain, very little is used directly by the plant; the greatest part runs off, or is evaporated into the atmosphere, whilst another part sinks into the earth and feeds the springs. There are but few observations oil the quantity of water needed by plants, but those that have made any pretensions to accuracy show that rain, after making allowances for that which flows away and is evaporated, does not supply more than a tenth part of what is necessary. It is unaccountable and inexcusable, that not a single botanist, since the time of Hales, should have taken up and carried on his important experiments on this subject.

The quantity of rain which falls in a given region, is not a measure of its fruitfulness; but the quantity of moisture, the absolute and relative quantity of vapor, which yearly, and especially during those months which are most important for vegetation, is contained in the atmosphere.

But water is not the only, nor the most important portion of the food of plants. They require carbonic acid gas, and the volatile salts of ammonia, which must be derived from the atmosphere; they are absorbed - the carbonic acid partly, and the ammoniacal compounds probably entirely, by means of the roots; clay and soil must be present as media to convey them to the plant. Though, in England, but half the quantity of rain falls that we find in a large portion of our country, the moisture of the air, and, consequently, with it the proper food, is more regularly and constantly supplied than in our arid regions. Coniferous, and other trees, flourish here better in situations where there is found to exist a succession of damp nights and mornings, as in regions where the dew is not dispersed till long after the rising of the sun.

Mr. J. J. Smith. - Dear Sir: I think you would confer a favor on horticultural societies, if you would publish a list of their corresponding secretaries, and thus enable them to exchange publications. Yours, very truly, Charles Gifford, Milwaukee.

It would doubtless prove useful to do so, and if the various horticultural secretaries will at once forward their names and residences, we shall with pleasure comply with the suggestion. Such a list, too, will, in fact, form a catalogue of existing horticultural societies in the Union and Canada. It shall appear in June or July, if all will forward the information.