THE MOVEMENTS OF PLAN'TS. 



191 



The latter are usually due to the [jrotrusion 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 o\'er 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 jjoint 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 ot 

 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 stri]:> between the half Fig iss.— a single 



^ ^ cell Irom a hair oi 



movinK up and the half moving down the chiUdonium. 



^ ^ ^ The arrows show 



\[ 



cell, which is also cjuiet. Such movements are 

 called rotation of the protoplasm. 



the direction of 



movement of the 



It is not protoplasm in the 



peripheral layer 



known whether either streaming or rotation and in the bands 



which separate the 



has any immediate relation to the well-being vacuoles. », the 



-' nucleus, with nu- 



cleolus. Highly 

 magnified. — After 



In addition to the mass Dippei. 



of the cell. 



280. Cell organs. 



movements of the protoplasm, the smaller protoplasmic bodies 



