SENSITIVE PLANTS. 377 



phenomena. It is to 'be remarked, however, that if the plant is kept 

 for a long period of time in darkness, it will ultimately expand its 

 leaves, and the phenomena of folding and opening will go on, although 

 at very in-egular intervals. 



The leaf of the Mimosa is sensitive of various kinds of stimuli, 

 such as shaking, wounding, burning, contact of irritating fluids, elec- 

 tric and galvanic shocks. Many chemical stimuli cause the leaves to 

 fold. Thus the vapour of prussic acid, of chloroform, and of ether, is 

 found to produce this effect ; and in such cases the irritability of the 

 leaves is either destroyed, or, at all events, a considerable period of time 

 elapses before it is restored. One or two drops of chloroform placed 

 on the base of the petiole make it droop, and cause the leaflets to close 

 in succession from apex to base. The influence extends to the other 

 partial petioles and their leaflets. Although the leaflets expand after- 

 wards, yet they are nearly insensible to the excitement produced by 

 touch. When chloroformised several times they at length lose their 

 contractility. Professor Simpson found that the vapour of chloro- 

 form affected the sensitive plant. If the vapour was either too strong 

 or too long continued, the plant was destroyed. When it was weak, 

 and applied only for a few minutes, the leaflets in some plants closed, 

 as when irritated, and did not expand again for an unusual length of 

 time. In other plants under exposure to chloroform, no closure of the 

 leaflets took place, and in a few minutes the plant became so anees- 

 thetised that the mechanical and other irritations of the leaflets and 

 petiole did not produce the common movements, nor did the irrita- 

 bility become restored for a considerable time afterwards. The 

 Yellow Water Sensitive plant (Neptunia plena), found in the East 

 and West Indies and in South America, exhibits irritability in its 

 petioles and leaflets. 



The temate leaves of many species of Oxalis (fig. 658) fold not 

 merely during darkness, but also when agitated or struck lightly and 

 repeatedly. Each of the leaflets folds upon itself, and then bends 

 downwards upon the common petiole. The plant called Desmodium 

 gyrans of the East Indies (fig. 659), the Gorachand of Bengal, or 

 Telegraph plant, has compound leaves, consisting of a large terminal 

 leaflet, and usually two smaller lateral ones. The latter are in con- 

 stant movement, being elevated by a succession of little jerks, until 

 they come into contact, and sometimes even slightly cross each other ; 

 after remaining in this position for a short time they separate from 

 each other, and move downwards by rapid jerks on opposite sides of 

 the petiole. This process is constantly repeated, and goes on in a 

 greater or less degree, both during day and night, but is most 

 vigorous during warm moist weather. The large terminal leaflet 

 undergoes movements also, oscillating very gradually from one side to 

 the other, and becoming horizontal or depressed. By the lateral 



