THE MOVEMENTS OF PLANTS. 



91 



The latter are usually due to the protrusion of processes from 

 the protoplasm through slits in the wall, as in many diatoms 

 (fig. 20). The filaments of the water slimes bend from side 

 to side, and so creep over wet surfaces very slowly (fig. 15). 

 Bacteria (fig. 17) and some diatoms move by means of cilia. 



II. Movement of protoplasm within a wall. 



278. Streaming. — In multicellular organs it is common 

 to find the protoplasm within each active cell 

 moving about from point to point within the 

 cell. The protoplasm is filled with numerous 

 large vacuoles, so that it forms a layer next the 

 wall, with threads or ribbons extending across 

 it (fig. 188). When currents start along the 

 wall and through the strands, the motion is 

 designated as the streaming of the protoplasm. 

 These currents along any particular portion of 

 the protoplasm may run side by side and in 

 opposite directions. 



279. Rotation. — When the protoplasm sur- 

 rounds a single large vacuole and thus occupies 

 only the periphery of the cell (fig. 181, C), 

 the whole mass may rotate, usually in the direc- 

 tion of its long axis. The portion immediately 

 in contact with the wall is motionless, and there 

 must necessarily be a strip between the half Fro 

 moving up and the half moving down the 

 cell, which is also quiet. Such movements are 

 called rotation of the protoplasm. It is not 

 known whether either streaming or rotation 

 has any immediate relation to the well-being 

 of the cell. 



280. Cell organs. — In addition to the mass 

 movements of the protoplasm, the smaller protoplasmic bodies 



-A single 

 cell from a hair of 

 C h e It doniunt. 

 The arrows show 

 the direction of 

 movement of the 

 protoplasm in the 

 peripheral layer 

 and in the bands 

 which separate the 

 vacuoles, n, the 

 nucleus, with nu- 

 cleolus. Highly 

 magnified. — After 

 Dippel. 



