784 MOVEMENTS IN THE CONTENTS OF CELLS. 
erroneously considered as a kind of rotation of the watery 
cell-sap ; but the very complete observations of Mohl have 
proved that it is due to a circulation of the protoplasm, which 
is rendered visible by the opaque granular particles which it 
contains (fig. 1142 a,c). The protoplasm thus circulating does 
not pass from one cell to another, but is strictly confined to the 
cell in which it originates. This kind of movement has been 
termed Rotation, Gyration, Cyclosis, or Intracellular Circulation: 
it ceases, in the generality of cases, in cells when they have 
attained a certain size, but in those of many aquatic plants it 
continues throughout their life. 
The appearances presented by these movements vary in 
different cases. Thus, in the cells of many hairs, as in those 
of the Common Spiderwort (Tradescantia virginica), the Potato 
(Solanum tuberosum) (fig. 40), and Althea rosea (fig. 1141), the 
protoplasm becomes hollowed out by a number of vacuoles 
filled with watery cell-sap, between which threads of protoplasm 
remain, and the motion is in reticulated currents radiating 
apparently from, and returning to, the nucleus; to this action 
the term circulation is applied. In the cells of the leaves of the 
Vallisneria (fig. 1142) and Anacharis, and in those of other 
parts of the same plants, intracellular movements may be 
readily observed when they are submitted to a moderate micro- 
scopic power ; here, however, the protoplasm becomes hollowed 
out by a single central vacuole filled with watery cell-sap, and 
passes with its granular contents round the interior of the walls 
of each cell, retaining its activity permanently ; which move- 
ment is called rotation. In the Characex, and especially in the 
Nitelle, which are transparent, the moving protoplasm does not 
rotate round the walls, nor in reticular currents, but passes 
obliquely up one side of the cell (fig. 1124) until it reaches the 
extremity, and then flows down in an opposite direction on the 
other side. 
No satisfactory explanation has yet been brought forward to 
account for this movement, but it is unquestionably connected 
with the vitality of the cell-contents, and Dr. H. de Vries be- 
lieves that it is chiefly instrumental in the transport of food 
material from one part of a plant to another. All agents that 
actually injure the cell will generally stop it at once, and perma- 
nently, though in some plants (as Nitella) a large cell may be 
tied across the middle with the effect of stopping the circulation 
temporarily ; but after a short time it will recommence in each 
half. The movements of the ciliated zoospores of the Algze (see 
page 395, and figs. 75-77), and those of the ciliated antherozoids 
of Algze (see page 397, and jig. 868), and of the higher Crypto- 
gamia (see page 566, and fig. 807), are usually regarded as ‘ ana- 
logous to the rotation of the protoplasm.’ 
4. Elaboration of the Cell-contents.—All cells exposed to light, 
heat, and air, which contain protoplasm, have the power of pro- 
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