Development, and Structure of the Vegetable Cell. 269. 
this would be scarcely possible, by reason of the peculiar condi- 
tions of their development: with others I have performed this 
task; and respecting the origin of the rest, I have assumed it to 
be analogous. 
Doubt has been thrown partly upon my observations, and 
partly upon the conclusions drawn from them. In order to 
complete the former by a detailed statement of the phenomena 
which most appeared to stand in opposition to my view, I will 
here especially demonstrate the free endogenous origin and 
growth of cork- and pollen-cells, and of the tissue-cells of the 
simple Algz, which have chiefly been cited as evidence of cell- 
formation by constriction; and I shall then consider myself 
justified in assuming that the same law applies also to the origin 
and growth of other cells. 
By the fuller elaboration and the solution of these questions, 
the conviction will be arrived at that the vesicular structure 
(which takes on at once the character of an active cell, and the 
properties of which are dependent on the peculiar relative com- 
position of its formative materials) progresses in a course of 
development determined by continuous changes in the physical 
and chemical condition of its membrane and cell-contents, therein 
resembling the organism at large, in the effectual working of 
which it has its own part assigned to it. 
By this means physiology will acquire the necessary basis for 
the right understanding both of the vegetative and animal func- 
tions of the organism, which it is now attempted to explain, in 
an equally one-sided and defective fashion, as the action of a few 
or individual physico-chemical forces governing the evolution of 
the cell. 
§ I. Development of Cork-cells. 
In Cecropia.—In Philodendron; in the cells of which they also develope 
manifold.— Porous, thickened cork-cells.—Restoration of their original 
spherical form by ammonia.—Absorption of their mother cells.—Growth 
of a cork-cell out of a cell into the neighbouring vessel.—Cork-cells in 
crystal-cells.—Cork-cells not developed in lacteal vessels and branched 
fibrous cells of the bark.—Cork-cells and callus-cells anatomically 
equivalent. 
The origin of cork-cells within those of the epidermis and 
bark has hitherto been ascribed by the few anatomists who have 
expressed a definite opinion upon this subject to the sudden 
appearance of a partition dividing the mother cell into two parts. 
This opinion has arisen from the circumstance that the mvesti- 
gations upon which it is based were made upon the cork-forma- 
tion of the bark, which does not present a favourable example, 
as in it the actual moment of the formation of new cells in the 
bark may easily be missed. 
