252 THE WONDERS OF VEGETATION. 



Every one is, of course, familiar with the singular 

 movement which the leaves of this plant show when 

 they are touched. At the gentlest contact, they shrink 

 back upon their supports ; these fall back upon the 

 common leaf-stalk, and the common leaf-stalk finally 

 upon the main stem. If the extremity of one of the little 

 leaflets be cut, the others close around it as if in sym- 

 pathy. The leaves of this plant are digitate, that is, 

 they are formed in rays branching oft' from a common 

 centre, like the fingers of a hand. The narrow, 

 straight leaves draw close to each other, as soon as 

 they are touched, till their upper sides meet. They 

 come together in the same way at nightfall, or when 

 a frost is sufficiently sharp to affect the plant. In 

 calm and warm weather, they are fully expanded; 

 but when the plant is shaken by the wind, all the 

 leaflets close simultaneously, and the leaf-stalks droop 

 together. Even a simple cloud passing over the face 

 of the sun, is sufticient to change their position 

 their expansion diminishing as light and heat de- 

 crease. Though closed, and apparently in a state of 

 sleep during the night, they shrink still more closely 

 together if any one touches them. At the junction 

 of the petiole with the stem, and of each leaflet with 

 the petiole, tiny glands are seen, which are the most 

 irritable points. To touch these glands with the 

 point of a pin, is enough to make the leaflet close. 

 If the shock is sharp, all the leaflets make in succes- 

 sion the same movement, and close two by two in 

 regular order. The whole leaf only begins to droop, 

 when all the little leaflets have closed up, as if the 



