S3 THIRD REPORT — 1833. 



The latter considers that the dotted tubes of Cycadece un- 

 doubtedly pass directly into the vessels called by the Germans 

 vasa scalarlformia \ but my own observations do not confirm 

 this statement. ' 



Circulation. — Whether or not plants have a circulation ana- 

 logous to that of animals, is a topic that was more open to con- 

 jecture at a time when the real structure of the former was un- 

 known, than it can be at the present day. Knowing, as we 

 now do, that a tree is more analogous to a Polype than to a 

 simple animal ; that it is a congeries of vital systems, acting 

 indeed in concert, but to a great degree independent of each 

 other, and that it has myriads of seats of life, we cannot expect 

 that in such productions anything absolutely similar to the mo- 

 tion of the blood of animals from and to one common point 

 should be found. The idea of circulation existing in plants 

 must therefore be abandoned ; but that a motion of some kind 

 is constantly going on in their fluids was sufficiently proved by 

 the well-known facts of the flow of the sap, the bleeding of the 

 vine, the immense loss plants sustain by evaporation, and by 

 similar phaenomena. The motion was for the first time beheld 

 by Amici, the Professor at Modena, who discovered it in the 

 Char a. He found that in this plant the cylindrical cells of the 

 stem are filled with fluid, in which are suspended grains of 

 green matter of irregular form and size. These grains were 

 distinctly seen to ascend one side of each tube, and descend the 

 other, after the manner of a jack-chain, and to be continually 

 in action, in the same manner, as long as the cell retained its 

 life ; the motion of the grains was evidently due to the ascend- 

 ing and descending current in the fluid contained within the 

 tube-like cell. It could not be ascertained that any kind of 

 communication existed between the cells, but each was seen to 

 have a motion of its own. 



The observations of Amici have been verified in this country 

 chiefly upon species of Nitella ; and from the investigations of 

 Mr. Solly, Mr. Varley, and Mr. Slack*, the nature of the phee- 

 nomenon has been determined with considerable precision. 



Among other things, it has been ascertained that in Nitella 

 the currents have always a certain relation to the axis of growth, 

 the ascending current vmiformly passing along the side of the 

 cell most remote fi-om the axis, and the descending current 

 along the side next the axis. 



Similar motions have been seen in several other plants. In 

 the cells of Hydrocharis Morsus-Ranae the fluid has been ob- 



» Transactions of the Society of Arts, vol. xlix. 



