OF THE ELEMENTARY STRUCT UKES. 



725 



3. Movements in the Contents of Cells. — In many cells, and 

 probably in all at a particular period of their life, when they 

 are in a vitally active state, a kind of movement or rotation 

 of a portion of their contents takes place. This movement is 

 sometimes erroneously considered as a kind of circulation or 

 rotation of the watery cell-sap, but the very complete observa- 

 tions of Mohl have proved, that it is due to a circulation of the 

 protoplasm, which is rendered visible by the opaque granular 

 particles which it contains (/^s. 1099 and 1100). The proto- 

 plasm thus circulating, does not pass from one cell to another, 

 but is strictly confined to the respective cells in which it origi- 

 nates. This kind of movement has been termed Rotation, 

 Gyration, or Intra-cellular Circulation. This movement 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 appeai-ances presented by these movements vary in dif- 

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



Fig. 1099. Fig. 1100. 



Fig. 1099. Three cells of one of the hairs 

 of the common Potato plant, showing 

 the circulation of the contents of each 

 cell in reticulated currents. In the cen- 

 tral cell the direction of the currents is 

 in part indicated by arrows. After 

 Schleiden. 



Fig. 1100. Cells of the leaf of VaUis- 

 neria spiralis, showing the circulating 

 current with its granular contents, pass- 

 ing up one side of each cell, across, and 

 down on the other side. The direction 

 of the currents is indicated by the arrows. 



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

 CSolanum tuberosum) (Jig. 1099), the circulation is in reticulated 

 currents, radiating apparently from, and returning to, the 

 nucleus. In the cells of the leaves of Vallisneria {fig. 385), and 

 in those of other parts of the same plant, intra-cellular movements 



3 A4 



