Liebig, in speaking of the inorganic constituents of plants, says: "Many of the inorganic constituents vary according to the soil in which the plant grows," etc. Again: "Most plants, perhaps all of them, contain organic acids of very different composition and properties, all of which are in combination with bases, such as potash, soda, lime, or magnesia," etc.; and after proceeding to show that certain acids are always, of necessity, present in plants, he proceeds: "It is equally certain that some alkaline base is also indispensable in order to enter into combination with the acids." And, while he seems to make it clear that the life and health of the plant depends invariably on certain acids, he says: "It will be necessary to bear in mind that any one of the alkaline bases may be substituted for another, the action of all being the same." His object is, if I understand him, to prove that certain acids are in the first place essential to the existence of the plant, and that this always attracts a given quantity of alkaline; that these alkalines are not necessarily the same, but similar in action; that the plant will take them up as they are found in the soil.

To prove this, he says: "It has been distinctly shown, by the analysis of D'saussure and Berthier, that the nature of a soil exercises a decided influence on the quantity of the different metallic oxyds contained in the plants which grew on it; that magnesia, for example, was con-tained in the ash of a Pine tree grown at Mont Brever, while it was absent from the ash of a tree of the same species from Mont La Salle; and that the proportions of lime and potash were also very different." Again he adds: "Let us now compare Berthier's analysis of the ash of two Fir trees, one of which grew in Norway, and the other in Allerard, (departemens de l'Isere.) One contained fifty, the other twenty-five per cent of soluble salts. A greater difference in the proportion of the alkaline bases could scarcely exist between two totally different plants".

Though it seems in all cases the oxygen was found nearly in the same quantities in each species, proving conclusively that while certain properties, such as some of the acids and oxygen, are always present in nearly uniform proportions, that it is not so with other substances; that they not only vary largely in quantity, but in some instances are altogether absent; that a tree, like an animal, has some latitude of choice in its food; and that the elements of the air are essential to the existence of both soils we find the tree to grow and flourish in. It may be questioned, if a tree, which finds the proper constituent particles in a soil for its healthy growth, can ever exhaust any part of it to such an extent as to produce death, if the natural sources of growth continue to yield their supply from the atmosphere. A forest does not wear out the soil and die; on the contrary, we are indebted to its agency for the virgin soil we find under its boughs. It is the opinion of writers of high authority, that among our modern forest trees, there are some which have attained the great age of four thousand years; and it is said that "investigation of coal and lignite strata has proved the existence of trees of the same order as those now existing." If this be true, it proves positively that trees do not draw on the soil, so as to destroy themselves, or to impair the perfect development of their seed and fruit.

But it may be said this is applicable to a state of nature. Well, this is just what I am endeavoring to show; that we have run contrary to this; and, from that cause, have produced an enfeebled race, which we are exposing to an uncongenial climate, and charging it (improperly, as I think), to the soil.

The. reason why soils are worn out, is because of injudicious cultivation, a continued removal of its products without a proper restoration of the properties thus removed. This is not applicable to trees, only so far as the removal of fruit is concerned, and the obstruction of the natural supply from decayed leaves, branches, etc. This may be larger or smaller, and of course it is wise to see that the soil is well supplied with all the particles thus drawn from it You may, however, feed the Pear tree as much as you please, and still it will die in the midst of a luxurient growth; and it is, there-fore, to other causes that we must look for its destruction, not to the want of proper food.

The advocates of the insect theory have not been very successful in proving its truth. They are bound to show something more plausible for its support, than the simple fact that insects are found in connection with the diseased parts. They are bound to show that these insects are really the cause, and not there as a result of the blight And, moreover, to show some reason why it is that they discriminate, pass by certain unmolested Pear trees, and do not make a clean sweep of all within their reach; and also, why it is that their destructive influence is sometimes suspended for years together.

Prof. Harris' description of the Scolytus pyri, in his invaluable work on Insects, which is mainly relied on as the support of this theory, fully defines its regular periods of change and operations. I am very sure that it will not apply to our blight, all the reasons for which I cannot here enumerate. Suffice it to say, that the injury of that insect "ends with the death of the branchy down to a certain point, but does not extend below the seat of attack, and does not effect the health of other parts of the tree." (Second edition Harris' Treatise on Insects). A comparatively harmless insect, whose effects all cultivators in this region will have observed on their trees.

I will here very briefly give what I deem the cause and the reason for the blight, which are not materially different from those given elsewhere. Long observation has ences. The Great Creator has in his wisdom to ordered it, that the vegetation, soil, and climate of every part of the globe act in perfect harmony, for the beet development of the former. A departure from this state of nature is at the hazard of the health and longevity of the plant or tree, though this result does not invariably follow. The Fear tree, as before observed, is not a native of this continent, but of a different hemisphere, where it grows to large size and great age, as other forest trees do. All intelligent writers, so far as I know, are agreed that the improvement of the fruit has generally been at the expense of the hardiness and durability of the tree, (not a necessary consequence). However, we find it so. We have imported an enfeebled race, and are exposing it to a new climate, the vicissitudes of which it is not fully capable of resisting. I care not for terms: whether you call it frozen sap blight, or sun blight; whether the effect is produced by sudden and rapid changes of winter temperature, or an excessive summer sun.