Fig. 3.—Morning-Glories.
The tips of all growing plants, like the first leaves that pierce the ground, move around; they are forever weaving their magic circles in the air; they take many hours sometimes to make a single turn, but they are as regular as the hands of a clock, and never forget and go backward. I have been watching some wistaria branches lately, and have been very much interested to see the new shoots, as they grew rapidly in the soft warm air, taking a slow turn around the wire placed to support them very much as you might wrap your arm about a swing rope to take a better hold. If there is a post or a wire near, you do not have to give your vines the twist they need to climb; they do their own twisting as they grow, and always in this quiet, deliberate way.
Fig. 4.—Virginia Creeper.
You have no doubt noticed that a Virginia creeper does not need a wire to climb by; it grows beautifully up any wall which has little unevennesses. Now look, if you can get hold of a new shoot, what the creeper has to help it along. It sends out tendrils that branch into many ends, and each one of these ends swells and becomes a sort of sticky pad, which glues itself to the wall (Fig. 4). These little pads, when they find no wall to fasten themselves upon, remain small, and finally wither away. Those on the vine in Fig. 4, which was trailing from a vine, are so, some small and some quite gone; but look at the pads in Fig. 5, which were detached from a painted board, and see how they look through the microscope. Very much like a boy's India rubber sucker, are not they? Some of these have the paint from the board still sticking fast on them. Others are all sparkling with the dried mucilage, which makes them look as if they had been sprinkled with sugar.
These little many-armed suckers give the plant a firm hold, while its head waves around until it touches some surface again, and again the pads lay hold for another upward stretch.
Fig. 5.—Pads through the Microscope.
There must be some curious arrangement by which plants, that can not feel and will as animals do, can move. They have no brains to think with, no nerves to feel with; it is strange to believe that they really do move with a reason. Mr. Darwin has examined the subject so closely that he has taken nearly six hundred good-sized pages to tell all he has found out about it. His ways of finding out are many. One method is this: he takes a small stiff bristle and glues it on the growing part of a shoot. By watching this shoot and comparing it with other shoots which had no bristle attached, he could not detect any difference in the movements. Above the little branch with the bristle attached he placed a piece of glass that had been smoked, so that the bristle, as it moved with the movement of the tip, would travel over the glass. He did not need to stand by and watch the branch; he could go away and attend to anything he chose, and when he came back there on the glass was a history of the travels the shoot had made, written by itself. He managed to hang up a sprouting bean or pea so that the root recorded its own movements in the same way. There were other ways which he used, all of them being ingenious, and requiring the greatest attention to get a correct map of their movements. He found that every plant in growing moved around as well as upward, but that some moved far more than others; the ones that grew tall and slender and needed support would send out shoots that swayed round in bigger and bigger circles until they could reach something to sustain themselves by, or else they would fall in helpless heaps on the ground.