16 VEGETABLE PHYSIOLOGY 
In a few cases, as in certain seaweeds, and in the sieve- 
tubes of the flowering plants, the connecting strands are 
sufficiently coarse to be visible under a comparatively low 
power of the microscope, and to need hardly any special 
preparation (fig. 18). 
It will no doubt have been noticed that the term ‘ cell’ 
is somewhat loosely used. A typical cell of a multicellular 
Coxtigvous CELLS oF THE ENDOSPERM GITUDINAL SECTION OF AN OLD AND 
or a Patm Seep (Bentinckia). Highly Stour Portion oF Ceramium ru- 
magnified. (After Gardiner.) brum, suowine CoNTINUITY BE- 
u, contracted protoplasm of a cell; b, a TWEEN THE PROTOPLASMIO CoN- 
group of delicate protoplasmic filaments TENTS OF THE AXIAL OR CENTRAL 
passing through a pit in the cell-wall. CELLS, uv, wu, AT THEIR Eps, AND 
LATERALLY WITH THE CoRTICAL 
Cretts 6, By Mrans oF Proto- 
PLASMIO THREADS. (After Hick.) 
plant consists of three parts—the protoplast, the cell-wall, 
and the vacuole (fig. 6); of these the first is the most 
important, being the living substance. A protoplast which 
has no cell-wall and contains no vacuole is still called a cell. 
The term is again often applied to a cavity which contains 
no protoplast, as in the case of old wood or cork. In such 
cases a protoplast once occupied the cavity, but it has been 
removed by death. These cells or cavities are consequently 
only the skeletons of dead protoplasts. 
