260 MR. C. DARWIN ON THE ACTION OF CARBONATE 
solved in the eell-sap, or, as in the present cases, is precipitated 
only through the action of certain reagents. 
On the view here suggested the exterior cells in many rows, 
some parenchyma-cells, and many or most of the endoderm-cells 
serve as receptacles for useless matter. It will, however, at first 
appear highly improbable that so many cells should serve for such 
a purpose. But this objection has no great weight; for in cer- 
tain cases a surprising number of cells may be found which, 
instead of containing chlorophyll-grains like the surrounding 
cells, are filled with crystalline masses of carbonate of lime and 
other earthy salts which are never redissolved. Many isolated 
cells or rows of cells likewise contain gummy, resinous, or oily 
secretions and other substances, which, it is believed, are of “no 
further use in the changes connected with nutrition or growth "*. 
We thus see that useless or excreted matter is commonly col- 
lected in separate cells ; and we thus get a clue, on the view here 
suggested, for understanding why the deposited granules and 
spherical masses are found in isolated cells or rows of cells, and 
not in the other cells of the same homologous nature ; and this 
is the circumstance which, as lately remarked, at first surprised 
me most. 
In the roots of plants the endoderm-cells commonly separate 
those of the parenchyma from the vascular bundle. Very little 
is known about their use or functions; so that every particular 
deserves notice. They resemble the exterior cells in their walls 
partly consisting of corky or cuticularized mattert ; and we have 
here seen that they likewise resemble the exterior cells by serv- 
ing as receptacles for the deposited granular matter, which, in 
accordance with our view, must be excreted from the inner paren- 
chyma-cells or from the vascular bundle. 
The fact of the granules being deposited in the exterior cells 
in one, two, or more adjacent longitudinal rows, which alternate 
with rows destitute of granules, is the more remarkable, as close 
to the tip of the root all the exterior cells are commonly gorged 
* Sachs, ‘Text-Book of Botany’ (Engl. transl.), 1875, p. 113. Also 
De Bary, ‘ Vergleichende Anatomie; pp. 142-143, When odoriferous oils or 
other strongly tasting or poisonous substances are deposited in cells, and are 
thus thrown out of the active life of the plant, there is reason to believe that 
they are by no means useless to it, but indirectly serve as a protection against 
insects and other enemies. 
t On the nature of endoderm-cells, see De Bary, * Vergleichende Anatomie,’ 
1877, p. 129. 
