SPONTANEOUS MOVEMENTS IN PLANTS. 289 



it. In the course of some hours it contracts into a spire, dragging up 

 the stem, and forming an excellent spring. All movements now cease. 

 By growth, the tissues become wonderfully strong and durable. The 

 tendril has done its work, and done it in an admirable manner." 



The phenomenon known as Sensitiveness is of by no means un- 

 common occurrence in the vegetable kingdom. It consists of a sudden 

 movement of the leaf, a portion of the flower, or the whole plant, on 

 contact with, or even on the approach of, a foreign body. One of the 

 most familiar examples is that of the Sensitive-plant {Mimosa pudica 

 and sensitiva), Figs. 5 and 6, in which three distinct movements are 



Fig. 6. 



observable when the leaf is touched by the hand or the warm breath. 

 First, the numerous leaflets close in pairs, bringing their upper faces 

 together, and also inclining forward ; then the four branches of the 

 leaf-stalk, which were outspread like the rays of a fan, approach each 

 other; at the same time the main leaf-stalk turns downward, bending 

 at its joint with the stem. The explanation offered in one of our best 

 botanical text-books, of this phenomenon, is. as follows: "There is a 

 swelling at the base of the petiole, the cells of which constitute, as it 

 were, two springs acting in contrary directions, so that, if the one from 

 any cause be paralyzed, the other pushes the leaf in the direction of 

 least resistance. These springs, if they be so called, are set in action 

 by the rush of fluid creating a turbid state of the one set of cells and 

 an empty state of the other. What circumstances regulate the turges- 

 cence are only imperfectly known." It will be obvious that, even if 

 this is correct as a statement of facts, it offers no real explanation of 

 the phenomenon ; for it is quite as difficult to understand how the mere 

 approach of the hand, which gives rise to a sensitiveness commencing, 

 it will be remarked, at the extremity of the leaf, will account for a 

 " turgescence " of the springs at the base of the leaf, which then causes 

 the movement. It should be observed also that we are unaware of any 

 use which these movements are to the plant. Similar sensitiveness 



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