In many discussions differences of opinions arise from failure of one side to grasp just what the other means. A good illustration of this is furnished by the following from the pen of Mr. Hovey to the London Garden: "Does the sap of trees freeze? This is a question which has been in dispute, and some of your contemporaries here do not believe in the theory. Under certain conditions, however, there can be no doubt the sap does freeze, and under others probably not. So far as sugar and starch freeze, just so far a tree will freeze; but the sap does freeze. I have had strong plants of Tea Roses frozen so hard as to split open the stem and the exuded sap to completely cover the wood with a coating of thin ice; and I cannot doubt that any tree before it has finished its winter hibernation will freeze when the cold is severe enough. There is a row of Lime trees on Boston Common which freeze so hard in our severe winters as to open the trunk for the distance of twenty feet or more from the ground fully one inch in diameter. I have put my hand in the crack. Yet these same trees in July would show no more signs of the opening than a mere vertical line of extravasated tissue.

I have recently read in the papers that trees in the Jardin des Plantes were split from top to bottom by the frost".

Now there is scarcely a person of experience in cold countries but has seen trees split from the top to the bottom by frost. If such persons still believe that " sap does not freeze," it ought at once to suggest that they understand by that something different from what the one understands who calls attention to the split trees.

Now what is really meant is that the sap in living healthy cells does not freeze. If it did, every tree in Massachusetts would be as surely bound to split as the "row of Lime trees on Boston Common." A hundred bottles of water set on " Boston Common " would all split if one did. Frost knows no such favoritism as smiting one row of bottles and letting all the rest alone-The action of frost is always uniform under equal circumstances. But in a tree only a few outer rows of the woody circles contain living cells. All the interior mass of wood in a tree is simply dead vegetable matter. There is no reason that we know why crude liquids taken into dead vegetable matter should not freeze, and, when it freezes, it will expand. Many persons have seen ice in small spaces found in the interior of trees cut in the winter season. This dead matter allows of some expansion, and the little moisture it contains may freeze without any perceptible effect on the whole body of the tree. But if the interior happens to be spongy, as is very likely to be the case with old Lime trees, and a great deal of water happened to be stored therein, we know of no reason why it should not freeze, and the trunk burst just as readily as it would in a bottle.

But all this is a very different question to that of the freezing of the sap in living cells, and for the cells to still continue thereafter to possess vital functions.