135 



the phenomenon termed catalepsy is produced in these species, 

 and M. Morren again arrives at the conclusion that this phae- 

 nomenon does not merely depend on a distinct property of 

 the cellular tissue, or on a want of elasticity in the flower- 

 stalks, but must be regarded in toto as a mechanical result, 

 independent of the position of the parts. 



M. Dassen*, who has published the beautiful memoir on 

 the motion of the leaves of plants, of which Prof Wiegmann 

 has inserted an extract in his journal, has drawn the attention 

 of botanists to a phenomenon of leaf-motion hitherto little at- 

 tended to. The leaves of those plants which move are fre- 

 quently provided with swellings at their base ; there are how- 

 ever other leaves which move without these swellings. The 

 motion of these latter again presents in various plants consi- 

 derable differences, which are more particularly described in 

 this memoir ; it consists in the inversion of their natural posi- 

 tion, which is sometimes performed in the space of a day, but 

 sometimes takes a much longer time. M. Dassen displaced 

 some branches of trees and various other plants from their 

 natural position, and bound them fast to the stem, so that 

 they hung downwards : in the course of a few days they had 

 spread themselves out so much, that the upper surface of the 

 leaves was again turned upwards. These experiments were 

 made in June when vegetation was in full force, and the re- 

 sult was the same in all cases. The experiments were then 

 repeated in October, when most of the branches remained 

 motionless ; only those of rose trees, of Robinice, and of her- 

 baceous plants endeavoured to regain their previous position. 

 The following question then presented itself: By what is 

 the motion of the branches effected, whether by a cause seated 

 in themselves, or by the leaves ? To determine this question, 

 M. Dassen repeated the experiments on branches with and 

 without leaves, and observed that those branches which had 

 been deprived of their leaves remained in their unnatural po- 

 sition ; the leaves were therefore regarded as the cause of this 

 motion of the branches. Subsequent experiments were made 

 in order to discover the mechanism producing the motion of 



* Onderzoek aangaande de Bladbewegingen, die niet door aanzwellingen 

 ontstaan. Tijdschrift voor naturlijke Geschiedenis en Physiologie, 1837,1V. 

 1. 2. p. 106 131. 



