MOVEMENTS. 199 



lining the walls and extending irregularly from side to side in 

 slender threads. At some one part the mass appears a little 

 denser than at others, and if the outline of this firmer mass is 

 at all well defined it is easily recognized as the nucleus (see 

 Fig. 2). 



546. Circulatioii of protoplasm in cells. Under a power of 

 300 diameters the delicate threads of protoplasm can be clearly 

 seen to have imbedded in them minute granules which are slowly 

 moving. It happens sometimes that a slight warming is re- 

 quired before any motion is apparent. When the current is fully 

 established, its different changes can be watched for a long time 

 without other disturbance of the specimen than that resulting 

 from the addition of water to replace that lost by evaporation. 



Two features of the motion require special notice: (1) the 

 granules do not pass from one cell to the contiguous one, but 

 remain confined in one ; (2) the threads in which the granules 

 move gradually change their shape and direction, growing wider 

 in one place and becoming narrower in another, while at the 

 points of contact with the lining of the wall the threads seem to 

 slip or glide very slowly, and accumulations of the protoplasm 

 here and there take place. The movement of the granules from 

 place to place in a steady current is called the circulation of 

 protoplasm ; the sluggish changes of the threads as they alter- 

 nately increase and diminish in size resemble the amoeboid 

 movements (see 555 and Fig. 175). 



547. In some examinations it is instructive to add a very 

 little glycerin or sugar to the water on the slide, in order to 

 cause a slight contraction of the protoplasm ; its whole mass 

 then appears as a shrunken sac, in the interior of which the 

 circulation can be detected. 



548. In a good specimen of the stamen-hair of Tradescantia 

 the protoplasmic currents are seen to course in slender threads 

 with a considerable degree of regularity. In some of the 

 threads or bands the currents go in one direction, in others in 

 another ; and it occasionally happens, as Hofmeister has pointed 

 out, that two opposite currents may pass in a single narrow 

 channel. 



549. There is more or less accumulation of protoplasmic 

 matter in the immediate vicinity of the nucleus, and there are 

 generally some slight projections into the interior of the cell. 

 The rate of circulation appears to be greater at the middle of 

 the threads than at the sides or ends of the cell. 



550. If these movements in a cell are compared with the 



