50 III. PROTOPLASMIC MOVEMENTS MICRO. DRAWINGS. 



centre of the cell-cavity, while the lining layer shows streams in 

 various directions. 



Rotation in Nitella. Th& strongest protoplasmic currents 

 known in vegetable cells are met with in the Characece (Stone- 

 worts). We must, however, take the genus Nitella, for Cham 

 has completely invested, usually calcified, and therefore opaque, 

 internodes, and it is the internodes which are specially suited for 

 study. For observation we select the younger branches of the 

 plant, and can see at once that the rotating layer of cytoplasm 

 has a considerable thickness. The outer layer of protoplasm 

 immediately lining the cell-wall, in which the chlorophyll grains 

 lie, is motionless. The motionless layer is here, therefore, com- 

 paratively thick, while it is in general so thin as to escape obser- 

 vation ; for in all the objects which we have already studied an 

 outermost denser portion of the cytoplasmic lining layer, the 

 Ectoplasm, takes no part in the movement. An obliquely wind- 

 ing stripe or band on the wall of Nitella is free from chlorophyll 

 grains ; it attracts the eye by its brightness. This colourless 

 band marks the neutral band in the protoplasmic stream. We 

 have here a repetition i what we found in the root-hairs of 

 Hydrocharis, where, however, the neutral band of the cyto- 

 plasmic layer was extremely reduced. The internodal cells of 

 Characece are multinuclear, the protoplasmic current carries 

 with it numerous elongated nuclei, which, however, show up as 

 brighter spots only in the most favourable cases. If the piece 

 of the plant is laid for 12 to 24 hours in 1 per cent, solution of 

 chromic acid, they can often be very readily seen, and their 

 peculiar rod-like, curved, and horse-shoe forms made out. Not 

 to be confused with these nuclei are the rounded balls of ap- 

 parently albuminoid matter which are seen carried around in the 

 stream in larger or smaller number, and appear either smooth or 

 with a spinous surface. Simultaneously with their movement 

 forwards, these balls are turned upon their axis, which shows 

 that the rapidity of the stream is greatest in that part of its 

 thickness which impinges on the stationary chlorophyll con- 

 taining outer layer of plasm, and gradually diminishes towards 

 the cell-cavity. If Nitella is laid in exceedingly dilute solution 

 of methylene blue, in a few hours, perhaps not till after a day, 

 these spinous balls are stained blue. As the streaming still goes 

 on uninjured, the blue balls are driven along by its means, and 

 form a very instructive picture. 



