CELL-LIFE. 



549 



Fig. 586. 



early stage in all other structures. This movement, which is erro- 

 neously called rotation of the cell-sap, is a circulatory movement of 

 the protoplasm made perceptible by the minute opaque granules 

 which exist in the colourless fluid. The nucleus is also carried 

 slowly along in this movement, which, when the protoplasm has 

 become converted into a mere network of 

 cords, has the appearance of a system of 

 reticular currents (fig. 586). This move- 

 ment of the protoplasm ceases in most cells 

 before they are full-grown ; but in many 

 aquatic plants, even of the class Phanero- 

 gainia, the protoplasm does not become 

 excavated in the same way as it does in 

 the cells of hairs &c., but applies itself 

 as a thickish layer upon the inside of the 

 cell-walls, and, retaining its activity, per- 

 forms a rotatory movement around the 

 wall of the cell permanently. In CTiara 

 the moving layer of protoplasm is not 

 applied upon the cell-wall : the primordial 

 utricle, with the chlorophyll-corpuscles 

 imbedded in it, lies on the cell-wall 

 motionless ; and a thick mucilaginous 

 layer, situated between this and the cen- 

 tral cavity filled with watery cell-sap, con- 

 tinually circulates. 



The circulation in reticulated currents is most easily observed in young 

 hairs of the higher plants. The movement of the parietal layer of proto- 

 plasm is made very visible in the leaves of Vallisneria by the green 

 chlorophyll-corpuscules imbedded in it j and it may be well seen in Ana- 

 charis, in the delicate tissues of Hydrocharis, Stratiotes, &c. It occurs in 

 the rootlets and other parts, as well as in the leaves. The phenomenon 

 is most strikingly shown in the Characefe, especially in the Nitdlce, which 

 are simpler and hence more transparent forms. 



This movement is only affected by substances that injure the healthy 

 condition of the structure, such as chemical agents producing bursting or 

 solution of the tissue, heat sufficient to cause coagulation or solution of 

 contents, &c. In Char a, the large cells may be tied across, and yet the 

 circulation be set up again in each of the chambers thus formed. Elec- 

 trical currents do not affect it. 



Causes of the Movements ; Action of Light. The movements in the 

 protoplasm are attributed to various causes according to the nature of 

 the movement, such as contraction of certain portions of it, varying 

 degrees of imbibition in different portions of the mass, the alternations 

 in this wise giving rise to the currents. The movements connected with 

 cell-division and growth and the rotation of the protoplasm take place in 

 darkness as well as in the light. In many cases it has been definitely proved 



Two cells of a hair of the sta- 

 men, of Tradescantia, with 

 nuclei and reticulated cur- 

 rents of protoplasm. Magn. 

 250diam. 



