224 Bibliographical Notices. 



sented 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 position ; 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 the leaves, whether the nerves 

 of the leaves remained during the process active or passive, &c., and 

 the following results were arrived at : that leaves with simple nerves 

 and without petioles change their position from the unnatural to the 

 natural as well as those with petioles ; and 2ndly, that the pa- 

 renchyma is the cause and not the nerves. Further observations re- 

 specting the mechanism producing the motion of leaves with and 

 without petioles gave the following results : 1 . All leaves with 

 simple veins have the power of self inversion ; 2. The apparently 

 unpetiolated leaves in which the veins are diiFused in a different 

 manner, move by a bend in their point of adhesion ; 3 . The short and 

 stiff as well as the long and slender petioles are unfavourable to the 

 motion ; 4. When the petiole is not too stiff or long, the inversion 

 of the leaves is produced by a semi-inversion lengthwise and also by 

 a bend of the petiole ; 5 . In/olia peltata the motion takes place partly 

 by a bend of the petiole itself, partly by a change in the direction of 

 the leaf with reference to the petiole. M. Dassen then proceeds to the 

 examination of the causes which produce the motion of leaves : va- 

 rious plants stationed in pots were left to grow turned from the 

 light, and some even without light in closed boxes. The result was 

 highly remarkable : the leaves of those plants which could not turn 

 themselves round died, but the remainder were inverted quite as 

 quickly in the dark as in the light, whence M. Dassen arrives at the 

 conclusion, that light was no more the cause of the direction of the 

 leaves upwards than darkness is the cause of the downward direction 

 of the root. Neither can the action of heat or that of moisture be re- 

 garded as the cause of this motion. Finally M. Dassen passes in 

 review those motions of the leaves which take place constantly in the 

 course of one day, and even without swellings ; these are the phe- 

 nomena which, as is well known, were regarded by Linnaeus as the 

 sleep of plants. M. Dassen considers Linnaeus's explanation as an 

 error into which that great man fell, as well as all those who have merely 

 copied almost word for word from him respecting this point. The 

 memoir On the Sleep of Plants, by E. Meyer, which I noticed in my 

 report for 1835, as highly interesting and full of laborious research, is 



