738 



PHYSIOLOGY. 



is sometimes erroneously considered as a kind of rotation of 

 the watery cell-sap, but the very complete observations of 

 Mohl have proved that it is due to a circulation of the pro- 

 toplasm, which is rendered visible by the opaque granular 

 particles which it contains {figs. 1107 and 1 108). The protoplasm 



Fig. 1107. 



Fig. 1108. 



Fig. 1107. Three cells of one of the hairs 

 of the coiiiniou Potato plant, showing 

 the circulation of tlie contents of each 

 cell in retlculMted currents. In the cen- 

 tral cell the direction of the currents 

 is in part indicated by arrows. After 

 Schleiden. 



Fig. 1108. Cells of the leaf of Vallis- 

 neria spiralis, showing tlie circulating 

 current with its granular contents, 

 passing up one side of each cell, across, 

 and di)wn on the other side. The di- 

 rectiDii of the currents is indicated by 

 tlie arrows. 



thus circulating, does not pass from one cell to another, but w 

 strictly confined to the cell in which it originates. This kind 

 of movement has been termed Botation, Gyration, or Intra-cel- 

 Jular Circulation : it ceases, in the generality of cases, in cells 

 when they have attained a certain size, but in those of many 

 aquatic plants it continues throughout their life. 



The appearances presented by these movements vary in dif- 

 ferent cases. Thus, in the cells of many hairs, as in those of 

 the Common Spider- wort {Tradescantia virginica), and Potato 

 {Solanum tuberosum) {fig. 1107), the circulation is in reticulated 

 currents, radiating apparently from, and returning to, the nu- 

 cleus. In the cells of the leaves of VaUisncria {fig. 1108) and 

 Anacharis, and in those of other parts of the same plants, intra- 

 cellular movements may be readily observed when they are sub- 

 mitted to a moderate microscopic power; but here, the proto- 

 plasm with its granular contents will be seen to pass round the 

 interior of the walls of each cell. Dr. Beale has figured the cir- 



