When a gardener first arrives in this country he is told that in a great measure he has his business to learn over again. This is a matter of surprise to him. Are not, he inquires, the principles of gardening the same all the world over? Knowing the theory of Horticulture, can I not. vary my practice to suit circumstances? This would be all very well if this "theory" were perfect, which unfortunately it is not yet found to be.

In nothing more have we been mystified by theory, or rather left to our own dark ways, than in .the matter of the best time to plant trees. After all that has been said and written, where are there two who will agree to any well defined principle? "I have found spring to be the best time." says one; "but," says his friend, " I have found autumn to be a better." Now if our theory were truly perfect, would there be any difference of opinion on this point? I think not.

All the aid we have received from physiological writers is, as stated by Lindley, by whom we are accustomed to swear, that, as the roots of plants grow in winter, except when actually encased in frozen soil, it is better to plant in fall and winter than in spring, because the extra supply of roots before the period of spring growth, renders the plant better able to meet the demands for moisture the foliage makes on it.

This theory is right in this, that it assumes the importance of preparing the fullest supply of moisture and food for an expected heavy demand; but it is faulty in supposing that that demand does not occur till spring. In England it would be right enough, but in America it is all wrong.

If we cut a branch from a tree, and expose it to a clear sun, it is dried up in a few hours; but if it be a foggy, misty time, it will not dry up as much in a day. So much depends on a dry or moist atmosphere. Evaporation rises from a living tree, as well as from a cut branch, and in proportion to the saturation of the atmosphere. In England, during the winter months, its atmosphere is as nearly saturated with moisture as possible, but in America, is nearly as dry as in summer. Indeed, it is a question whether it is not dryer in our severest frosty days, than it ever is- under our blazing midsummer sun. Hence a living tree in England would be storing moisture every day during winter, while the same tree in America may have it drying out faster than it comes in by the root.

In choosing the best time to plant trees, therefore, we have to make it, as I have said in my Handbook of Trees, "a question of evaporation," rather than one of growth by the roots merely. Then we can understand the varying success of different individuals with different seasons, which before seemed unaccountable. One man plants a quantity of hemlocks or junipers in November; the roots commence to grow at once, but also at once, sets in a dry cold " spell," and the moisture evaporating faster than it comes in, the plants dry up, are in fact "scorched," as truly,'literally, scorched as if by the influence of a July sun. He goes at it again in spring, a moist time ensues, not rainy, perhaps, or even foggy' but a genial, mild, "even tempered" time, and they succeed. Then the time, not the circumstances, suggests itself, and with him there is no time to plant like the spring. Not so with his neighbor; he also planted in November; "didn't take any particular care either." For a few days there was so much moisture in the atmosphere that the roots had time to "get a fair hold" before moisture was much wanted.

The winter was not severe - twenty or thirty degrees of frost were not day after day bringing the moisture to the Surface of the branches by expansion, and on the south side the sun drying it off as fast as it froze out - they had nothing of all this to endure, and they succeeded. You don't catch my friend planting hemlocks and junipers at any other time than the fall or winter after this. And so it goes, the world outside all the while exclaiming: "How the doctors disagree." '

The subject is capable of much further elucidation. What I have said will, however, be sufficient to show that to know when best to plant trees, will require us to study more than we have done, how to promote or check evaporation.