REPORT ON THE PHILOSOPHY OF UOTANY. 3.'> 



served to move round and round their sides in a rotatory man- 

 ner, which, however, has not been seen to follow any particular 

 law. In the joints of the hairs of Tradescantia virginica 

 several currents of a similar nature exist ; and in the hair of 

 the corolla of a species of Pentstemon, Mr. Slack has observed 

 several currents taking various directions, some continuing to 

 the summit of the hair, whilst others turn and descend in va- 

 rious places, two currents frequently uniting in one channel. 



It may hence, possibly, be assumed that in the cells of plants, 

 when filled with fluid, there is a very general rotatory move- 

 ment, which is confined to each particular cell. This, it is ob- 

 vious, can form no part of the general circulation of the system, 

 which must often occur with great rapidity, and which must 

 take place from the roots to the extremities. The rotatory 

 motion may perhaps be considered a sort of motion of di- 

 gestion, and connected with the chemical changes which matter 

 undergoes in the cells from the united action of light, heat, 

 and air. 



What has been supposed to be a discovery of the universal 

 motion of sap has been made by Professor Schultz of Berlin, 

 who remarked two torrents, one of which was progressive, and 

 the other retrogressive, in what he calls the vital vessels (ap- 

 parently the woody fibre) in the veins of Chelidonium majiis, 

 and in the stipulae of Ficus elastica. 



His observations have been repeated by a Commission of the 

 Institute, composed of MM. Mirbel and Cassini, who have 

 reported * that they have also seen the motion described by 

 Professor Schultz ; and I have myself witnessed it as is repre- 

 sented by those observers. But it appears probable, from se- 

 veral circumstances, that the motion that has been seen has 

 either been owing mei-ely to the vessels in which it was re- 

 marked having been cut through, and emptying themselves of 

 their contents, as Mr. Slack has suggested, or else was nothing 

 but the common rotatory motion imperfectly observed. 



Strvcliire of the Axis. — From the period when INI. Desfon- 

 taines first demonstrated the existence of two totally distinct 

 modes of increase in the diameter of the stems of plants, it has 

 been received as a certain fact that monocotyledonous plants 

 increase by addition to the centre of their stem, and dicotyle- 

 donous by addition to the circumference. Nothing has yet 

 arisen to throw any doubt upon the exactness of this notion in 

 regard to dicotyledonous plants ; but Dr. Hugo Mohl has 

 endeavoured to showf that monocotyledonous stems are not 



* Annalfs ilen Sciences, vol. xxii. p. 80. 



t Molil, "])(.■ ralnianim Stnictura," in Martius's Genera et Species Palmnrvm. 



1 83('j. D 



