THE LIVING CELL 
39 
Other physiological characteristics, as motility and con- 
ductivity, might be added, but 
most satisfactory criteria by 
which living may be distin- 
guished from non-living matter. 
PROTOPLASMIC MOVEMENT 
Living matter in its active 
state of existence exhibits motion. 
The several kinds of movement 
of protoplasm which may be 
observed within the closed cells 
or in naked cells are amoeboid 
movement, ciliary movement, cyto- 
plasmic rotation and cytoplasmic 
circulation. Cold retards and 
heat accelerates movement with- 
in certain ranges. : 
1. Amoebotd movement a 
creeping or flowing movement 
‘such as is typical of the plas- 
modium or vegetative body of 
slime molds and of the animal 
Amoeba. 
2. Ciliary movement can be 
observed in the motile bacteria 
and in the sex cells of the lower 
and some of the higher plants 
which possess slender proto- 
plasmic outgrowths called c7lza 
which lash the water. 
3. Cytoplasmic rotation is well 
illustrated in Elodea and Nitella, 
two common aquarium plants. 
In rotation, the protoplasm 
is 
the four just discussed are the 
Fic. 20.—A, embryonic cells from 
onion root tip; d, outer plasma mem- 
brane; c, cytoplasm; a, nuclear mem- 
brane enclosing the thread-like nuclear 
reticulum 4, nucleolus; ¢, plastids (black 
dots scattered about). 8B, older cells 
farther back from the root tip. The 
cytoplasm is becoming vacuolate; /f, 
vacuole. C, a cell from the epidermis 
of the mid-rib of Tradescantia zebrina, in 
its natural condition on the right, and 
plasmolyzed by a salt solution on the 
left; g, space left by the recedence of the 
cytoplasm from the wall; the plasma 
membrane can now be seen as a delicate 
membrane bounding the shrunken 
protoplast. All highly magnified. 
(Stevens.) 
moves down one side of the cell then across the end and returning 
along the other side and end. In Elodea the chloroplasts found 
