I must be a poor, very poor, physiologist, since, with all my patience in reading over and over again and trying to understand something about the article "on the excretion of plants," published in your February number, I know not much more than before; that is to say, I do not understand of what importance it would be to agriculture, etc, to know with certainty that the excretions of plants are poisonous to the soil. Would that certitude render the soil any better for raising crops, without any antidote to the poisonous excretions - I mean without any manure! If so, the excrementitious doctrine is good to know, and I will likely agree with Dr. LINDLEY and others.

One more question: - Is any one who understands that soils become exhausted, by being constantly cropped with one kind of plant, a physiologist! If so, we are all more or less physiologists. Whether, that besides this knowledge, we should believe, with some, that the deterioration of the soil is caused by the doubtful deleterious excretions of the roots, or by their more probable excessive absorption of the nutritive gases; or, with some others, that sourness is only the result of an acid, without any doubt caused by a superabundance of water!

Let us suppose now, that we should all be of one opinion about those physiological subtil ties, where would be the good of it! Would the soil be more or less fertile! No! Then wherefore those digressions about finding a knot in a bulrush. If the advocates of those two different doctrines should give us the means of re-establishing the fertility of deteriorated soils, whether the exhaustion be the result of poisonous excretions or enervating absorption, some good might be effected. But no, the only thing we get from those doctors' arguments are quotations from all quarters, all probably very exact, but which taken together, in my opinion, would not be as good for any poisoned soil as simple rotation of crops, deep tilling, and animal excrements; and draining and frequent hoeing for the acid or sourness. Simplex - Albany, N. Y.

We have great faith in the efficiency of rotation of crops, drainage, deep Ullage, manures, and general good culture, for exhausted or defective soils. Nevertheless, we cannot treat a question that has deservedly attracted so much the attention of ardent philosophic minds, and one that however unsettled it may be has an important bearing on cultivation, so lightly as our correspondent "Simplex" appears to do.