158 IMPATIENS. KALMIA. [BOOK n. 



measurement, that the diameter of the central cavity is less 

 after the bursting of the fruit than before. 



The valves of Impatiens noli-tangere, when the fruit is 

 ripe, separate and spring back with great elasticity when 

 touched. In this case the phenomenon is apparently capable 

 of explanation upon a similar principle to the Elaterium. In 

 the fruit of Impatiens, the tissue of the valves consists of 

 cellules that gradually diminish in size from the outside to 

 the inside; and the fluids of the external cellules are the 

 densest. The latter gradually empty the inner cellules and 

 distend themselves ; so that the external tissue is disposed to 

 expand, and the internal to contract, whenever anything 

 occurs to destroy the force that keeps them straight. This 

 at last happens by the disarticulation of the valves, the 

 peduncle, and the axis; and then each valve rapidly rolls 

 inwards with a sudden spontaneous movement. Dutrochet 

 proved that it was possible to invert this phenomenon by 

 producing exosmose : for that purpose he threw fresh valves 

 of Impatiens into sugar and water, which gradually emptied 

 the external tissue, and, after rendering the valves straight, 

 at length curved them backwards. 



In Kalmia the anthers are retained in little niches of the 

 corolla ; and, as soon as they are by any cause extricated, the 

 filaments which had been curved back recover themselves 

 with a spring. In certain orchids, of the tribe called Vandeae, 

 the caudicula to which the pollen masses are attached will 

 often, upon the removal of the anther, disengage itself with a 

 sudden jerk, like a spring from which the pressure is removed. 



For numerous observations upon other cases of vegetable 

 irritability, see Dutrochet's Memoires previously quoted, in 

 which there is much speculation upon the subject. 



In conclusion, mere hygrometrical action must be men- 

 tioned as the cause of some phenomena wholly independent 

 of vital action. Dr. Lankester thus describes them in 

 Funaria hygrometrica. " If one of the dried setae be taken 

 in the hand, and its lower portion moistened with the finger, 

 the capsule will be seen to turn from right to left, making 

 two, three, or -even more complete revolutions; if now the 



