152 



MOVEMENTS IN CELLS — EOTATION. 



times the plant consists of a single central cell ; at other times there are 

 several smaller ones surrounding it, which must be removed in order 

 that the movements which occur in the central cell may be seen. Many 

 of the species are incrusted with calcareous matter, and thus become 

 opaque, while others, as Ohara or Nitella flexilis, have no incrustation, 

 and are transparent. Those plants with unincrusted tubular , cells 

 best exhibit movements. In these plants the movements take place 

 between the two membranes of which the cell- wall is composed. They 

 are not interrupted when a division of the cell has been made by 



c 



\*«<f^ 



r 



Fig. ■2U. 



Fig. 245. 



means of a ligature ; an evident movement may still be observed in 

 either section. Some granules, of a green colour, are attached to the 

 cell-wall, while others are carried with the current which passes along 

 one side and returns by the other, following an elongated spiral direc- 

 tion. In the cells of the branches the descending current is next to 

 the axis. In %ure 244 the course of the currents in different cells 

 is indicated by aiTows. 



In Vallisneria spiralis (which includes V. Micheliana and Jac- 



Fig. 244. A small portion of a Clara, magnified to show the intracellular circulation. 

 The arrows mark the direction of the fluid and granules in the different cells. The clear 

 spaces are parts where there is no movement. The circulation in each cell is independent 

 of that in the others. Fig. 245, Large internal cell of Vallisneria, showing the direction of 

 the currents in intracellular rotation. There is an occasional nucleus seen in the course 

 of the circulation along with the chlorophyll grains. 



