THE GENERAL STRUCTURE OF PLANTS 7 
neria, Nitella, Elodea (fig. 7), and others, a streaming move- 
ment of the granules the protoplasm contains can be detected 
Fic. 7.—CELLS FROM THE LEAF oF 
aw 
Elodea. x 500. Fie. 8.—Two CELLS FROM A 
A . Stammvat Harm or Trades- 
n, nucleus; p, protoplasm, in which x 
are embedded numerous chloro- cantia. X 300. 
plasts. The arrows show the The arrows show the direction 
direction of the movement of the of the movement of the proto- 
protoplasm, plasm. 
under a high power of the microscope. In other plants of 
terrestrial habit, e.g. certain cells of Tradescantia and 
Chelidonium, a similar streaming of 
the protoplasm is observable (fig. 8). 
Such movements are spoken of as 
rotation when the current flows uni- 
formly round the cell, or as circu- 
lation when the path has a more 
complicated course. 
It has been mentioned that, with 
very rare exceptions, all cells con- 
tain a specially differentiated portion 
of protoplasm, known as the nucleus 
(figs. 6 and 9). This structure does 
Fia. 9.—NvoLEus oF A CELL, 
SHOWING ARRANGEMENT OF 
THE CHROMATIN THREADS. 
x 1000. 
a, threads; 6, nucleolus. 
not occupy a very definite position in the cell, but not 
infrequently is found almost in the centre. If the whole 
