The model was constructed of glass tubes, closed at one end with a piece of bladder, and joined together in series by means of thick-walled caoutchouc tubing; the top which represented a leaf was a funnel closed by a bladder. This artificial cell chain was filled with water, mixed with carbolic acid to keep the pores from clogging, and was set up with its base immersed. The fluid evaporated through the membrane at the top of the funnel, which drew up more from the cells below, the space so caused being continually filled from the base. This is an interesting experiment and is said to solve the question, but it is open to the same objection, that a tree will not absorb fluid and carry it for any length of time after the roots are cut off. I regard it, however as a long stride in the right direction.
To what source, then, must we look for an explanation of this process?
I think it is a fact that the small, new root-fibers imbibe fluid with considerable force, but it is undoubtedly a fact that they soon lose this force when deprived of the leaves; that the leaves with the aid of evaporation, exert a great force, which the above experiment plainly indicates; and I cannot consistently dismiss the idea that capillary attraction has something to do with it. If we also add to this the theory that the swaying of the stems and branches by the wind is continually changing the shape and size of the cells and is thus driving the juices wherever an opening will allow them to travel, thus bringing the elasticity of the tree to our aid, we have again advanced.
But the principle of life is not discovered. Whenever it is we may find it to be a force much greater than any we have so far examined, and which may even cause the overthrow of all theories heretofore advanced.
EMERSON AND THE WOODPECKER STORY.
NO squirrel works harder at his pine-nut harvest than the carpenter woodpeckers in autumn at their acorn harvest, says John Muir in the December Atlantic, drilling holes in the thick, corky bark of the yellow pine and incense cedar, in which to store the crop for winter use; a hole for each acorn so nicely adjusted as to size that when the acorn, point fore-most, is driven in, it fits so well that it cannot be drawn out without digging around it. Each acorn is thus carefully stored in a dry bin, perfectly protected from the weather, a most laborious method of stowing away a crop, a granary for each kernel. Yet they never seem to weary at the work, but go on so diligently they seem determined that every acorn in the grove shall be saved. They are never seen eating acorns at the time they are storing them, and it is commonly believed that they never eat them or intend to eat them, but that the wise birds store them and protect them solely for the sake of the worms they are supposed to contain. And because these worms are too small for use at the time the acorns drop, they are shut up like lean calves and steers, each in a separate stall, with abundance of food to grow big and fat by the time they will be the most wanted, that is, in winter, when insects are scarce and stall-fed worms most valuable. So these woodpeckers are supposed to be a sort of cattle-raiser, each with a drove of thousands, rivaling the ants that raise grain and keep herds of plant lice for milk cows. Needless to say, the story is not true, though some naturalists even believe it. When Emerson was in the park, having heard the worm story, and seen the great pines plugged full of acorns, he asked (just to pump me, I suppose): "Why do woodpeckers take the trouble to put acorns into the bark of the trees?" "For the same reason," I replied, "that bees store honey and squirrels nuts." "But they tell me, Mr. Muir, that woodpeckers don't eat acorns." "Yes they do," I said. "I have seen them eating them. During snowstorms they seem to eat little besides acorns. I have repeatedly interrupted them at their meals, and seen the perfectly sound, half-eaten acorns. They eat them in the shell as some people eat eggs." "But what about the worms?" "I suppose," I said, "that when they come to a wormy one they eat both worm and acorn. Anyhow, they eat the sound ones when they can't find anything they like better, and from the time they store them until they are used they guard them, and woe to the squirrel or jay caught stealing."