LIFE OF THE PLANT-CELL. 



93 



uncovered. If the cell be carefully tied across, the current is in a short 

 time re-established in each subdivision. If the cell be cut through, the 

 circulating fluid escapes only on one side from the stream which is directed 

 towards the opening, the remainder of the fluid completing its entire 

 circuit through the cell before it also comes to escape. Any influence 

 detrimental to the life of the plant also affects the motion of the sap, and 

 whatever favours the former also promotes the latter. The same thing, 

 in all respects, takes place in Chara, only that in this plant the observa- 

 tion is not so readily made. In no plant in which the circulation is in 

 any way exhibited are the currents found to be so associated as to 

 constitute an ascending and a descending spiral. In Hydrocharis, 

 owing to the perfect transparency of the naturally isolated cells of the 

 hairs of the roots, the observation is exceedingly easy. In Vallisneria 

 (figs. 95, 96.), although the leaf must first be cut parallel to the surface, 

 in order to render it sufficiently transparent for convenient observation, 

 this proceeding is not detrimental to the motion, which, after a few 

 minutes, is again exhibited in its pristine activity. In this plant the 

 circulating mucous fluid is very scanty, and constitutes merely a very 

 thin covering on two opposite walls ; but it has sufficient power to carry 

 on the usually flattened lenticular granules covered with chlorophyll, 

 and which are of tolerable size. 



95 A, Section parallel to the surface from the leaf of Vallisneria spiralis. In the cells 

 from a to e is seen the current of sap, the direction of which, as observed in each cell, 

 is indicated by the arrow. In the cells marked 6, which form the lateral boundaries of 

 the air-passage opened by the section, the anterior half only of the current is seen in 

 its whole width. The very gelatinous cytoblast circulates with the stream. B exempli- 

 fies the same section on a ground plan. 



96 A portion from the section shown in fig. 95. more highly magnified. The thick- 

 ness of the stream exceeds that of the double cell-wall : the elongated, roughened 

 corpuscles are the lenticular granules of chlorophyll carried along with the current ; 

 at the same time their varying figure and various positions in the circulating fluid 

 are exhibited. 



