376 Hitcucock: DIFFERENTIAL STAINING 
of denser cytoplasm, carrying small, uncolored granules and some 
spherical plasmic bodies in suspension, in active cyclosis, closely 
following the cell wall. This outer layer, which, for convenience, 
may be here specifically designated as protoplasm, is quite un- 
colored. Thus we have, if we imagine a cross section, the cellulose 
wall lined with the chloroplasts in a thin, reticulated stroma, 
then the thin layer of uncolored, moving protoplasm, within which 
is the strongly colored, wide cylinder. 
The line of demarcation between the colored cylinder and the 
uncolored protoplasm is as sharply defined as a thin cell wall. 
Clearly it is the so-called vacuole wall. This line is wavy and 
constantly changing as it yields to the irregularities in the thick- 
ness of the protoplasm stream. The stained contents of the 
vacuole participate, however, in the movement of the protoplasm 
without, following precisely the same course. Moreover, deep 
within the vacuole it may be observed that the neutral or indif- 
ferent line, which marks the separation of the currents moving in 
opposite directions, indicates also an invisible barrier within the 
vacuole, which cannot be easily crossed by stray elements from 
the circulating stream. 
A sharply defined differentiation of the cell contents has thus 
been effected. The significance of it is not yet clear. It is not 
possible at present to state precisely what particular parts or 
elements in the cell sap have taken the stain, or whether any 
color is held in solution. By far the greater number of the cor- 
puscles or spherical elements so evident in the circulating stream 
of charas, are suspended in the cell sap, not in the protoplasm. 
The Schleimblaschen of Naegeli, later named Wimperkorperchen 
and mentioned by Allen as ‘‘ciliated”’ granules of protoplasm, are 
often deeply stained, but apparently not always. The name is 
misleading since there is no evidence of the presence of motile 
cilia on these bodies. 
We have some admirable hypotheses concerning osmotic action 
in the plant cell. There are membranes permeable and selec- 
tively permeable, solutes obedient to the rules established for 
their guidance, whereby the whole train of physical phenomena 
becomes clear. It now becomes desirable to know how the coloring 
matter makes its way into the vacuole of the Nitella cell. The 
