The minds of horticulturists in this prairie country are very much exercised over the seeming fact that apple orchards must be renewed every fifteen or twenty years, and the question naturally suggests itself, why this short life and early decay, when forest trees seem as healthy and as long-lived as in other countries ?

The hypotheses advanced to account for this state of things, vary as much as do specifics for pear-blight or hog-cholera. One man thinks the trouble is climatic, and another thinks it is something in our soil, or something lacking in the soil; others think it is caused by the present mode of propagating the apple tree by root-grafting, pasturing our orchards, close planting, low-branched trees, and high-topped trees, etc., We often hear of apple trees in the Eastern States and in Canada living and producing bountifully for a hundred years or more, and just in their prime at forty or fifty years old. Is this a fact ? and, if so, what varieties attain to such longevity? Is it the improved varieties, or the seedlings of ye olden time ?

Can you give us any information in regard to the short career of our apple orchards ?

[There is little doubt but the average life of an apple tree in Pennsylvania is about fifty years.

The length of life in any tree depends on its vital power. The English oak, in England, has an average of 500 years. In America, its average, so far as the few instances known will allow us to judge, is but about 100. The apple, we believe, has about the same comparative duration in the two countries.

Anything that affects the vital power of a plant affects its longevity. A tree which has to struggle with high winds and a low temperature, will not live nearly as long as the same kind of tree protected from these trying circumstances. In like manner, one subjected to very dry or very wet influences, or anything that is not the most favorable to vegetation, will not live as long as one which has everything favorable about it.

Thus we see that all the hypotheses named by our correspondent may have an influence so far as they bear on this question of vital power. Climate, soil, management, all relate to the question. We could make trees live as long in Illinois as anywhere else, but it would probably be at the expense of something we prize. What we call culture, is usually opposed to abstract laws of health in plants. We want something which nature unaided would not give us, and she insists if we will have it, it shall be only at the expense of something else. It may be that we have the best of it, even with a shortened longevity. This is the practical as against the abstract question. - Ed. G. M].