The question has been mooted, " is tan-bark a fertilizer," in one of the late numbers of the Horticulturist. Mr. Doweing speaks highly of it as a mulcher for strawberries; and on the authority of Prof. Mapes, recommends it as a fertiliser, for that plant. Its good qualities as a mulcher, I can well understand, it being a nonconductor; and therefore a protection against the cold of winter, and the too sudden heat of early spring, guard* ing against great alternations of weather allowing the cold soil after winter to become gradually warmed, preventing that rapid change from cold to heated ground, but blending the one season gently into the other.

As a fertilizer for strawberries, Prof. Mapes has found it excellent. For this purpose I have not tried it myself, but with many other plants and trees I have. I must, however) in the outset, soy what I have used, was not freth from the tan-yard, but had been used for the forcing of pines, grapes, and other purposes, and after all fermentation had ceased. I employed It In various ways-among others the following: I have mixed it with soil (a sandy loam) in which were planted out American Arborvitss, Chinese do., English laurels, laurestinus, Portugal laurels, Evergreen oaks, Arbutus, Daphnes, and many other shrubs - and in it not one genera grew well. Indeed, on the contrary, it gave undeniable evidence of being most inimical to the growth of them all; the first year after planting they put on a debilitated sickly appearance; the second year they became worse, after which the plants were moved into other ground to save them; a considerable part was so sickly they had to be thrown away. In order to test this more accurately I had a bed about 100 feet long, five feet wide, taken out to about the depth of 18 inches, and filled with old tan-bark; in this was planted a collection of shrubs including nearly all that I have already named with many others; the greater part were turned out of pots and were healthy, thrifty plants; consequently they received no check on their removal- This was performed early in April - an excellent time.

The first summer, if it could hardly be said these plants grew at all, they did very miserably, turning as yellow as a lump of Catifomian gold, and autumn found them half decayed and dying. Here, however, they were allowed to remain - -grow they did not - another year - at the end of which more than three-fourths were completely dead,and of the few which remained, only portions of the plants were alive. They were in such a lamentable plight that the whole had to be destroyed without a solitary exception, and the bed filled in with the original soil. From the shrubs used, the reader will readily know these trials hare been made in England. Tan-bark at this time, had been strongly recommended as a fertilizer for the Chinese Arborvi-tae, and in my experiments it proved as fatal to that shrub as the others. For Rhododendrons I have employed it in a variety of ways, such as mixed with peat, mixed with loam, and also planted them into it in a pure state; in all of which it proved injurious, and had to beremeved. Upon many other shrubs and trees I have tried it by digging it into the ground and the effects were the same, as well as on kitchen garden vegetables. I have seen it tried as a top dressing upon grass land, and its effect! were most injurious.

It destroyed and weakened the best varieties of grasses, and, as a consequence, gave more room for the weeds; its effects were visible at some distance. Having had annually at command a large quantity of eld tan-bark and this for some years, I have experimented with it,in a variety of ways en a large collection of trees and shrubs, as I have been describing, in an extensive nursery, without any beneficial results. In the spring of every year, the pmnings, weeds, rubbish and cleanings of the nursery were regularly charred, and it was at last determined to char the tan-bark too. After which it is found to be useful as a fertilizer for heavy land, or seeds, seedling trees, cuttings, or any thing requiring a light manure.

From the above facts it is evident tan-bark must be used with caution. Perhaps there may be a difference between what I have used - what had undergone fermentation in pits and hot-houses - and what other persons may use fresh, from the tan-yard, hut surely if there is a danger with either, I should consider tin greater with the latter; it being used in a rank state. Tours respectfully, JohnSaul. Wash-ington, D. C, April 16,1852.

[We quite agree with Mr. Saul as to any practical value of tan-bark as a manure. To nearly all plants it is no doubt injurious - especially if fresh - though possibly it may be hene-ficial to strawberries if spread lightly over the beds.

But as a mulcher, to keep the soil cool and moist in this sunny climate, tan-bark is a most invaluable substance for almost every tree or plant that needs such protection. As a winter protection- against cold we have found it equally serviceable~-especially if kept dry by a coating of straw or boards to shed the rain. While therefore, we doubt its value as a fertilizer generally, and are confident if brought in contact with the roots of many plants it is injurious-, we look upon it as of exceeding value as a pro lection against the excesses of our climate In all eases where such is necessary. En].