270 Prof. H. Karsten on the Formation, 
The statement given by meas to the mode of production of cork, 
in my investigation of Cecropia peltata, Linn. (Acta d. Akad. d. 
Naturf. xxiv. pt. 1. p. 86) has not been taken into consideration by — 
my successors. In this plant, in the outermost lamima of a collen- 
chymatic tissue covered by the epidermis, and at the commence- 
ment of the second period of vegetation, I observed the forma- 
tion of some small cells, filled with colourless fluid, in contiguity 
with the chlorophyll-vesicles. These colourless cells develope 
themselves, in the peripheral cells of the lamina in question, into 
cork-cells simultaneously with the absorption of the chlorophyll, 
and in those on the central aspect into parenchyma-cells of the 
bark, in which cork-cells are subsequently formed in the same 
manner. 
Less difficulty is experienced in the observation of the forma- 
tion of cork-cells when this tissue is developed in the process of 
cicatrization after an injury to a stem, by which the normal 
functions have been suddenly arrested—a circumstance partially 
studied by Mohl in his memoir on the process of cicatrization 
in plants (Botanische Zeitung, 1849, sp. 641). Hitherto I have 
been most successful in following up the history of the develop- 
ment of cork-cells in all its stages in the commonly cultivated 
Philodendron pertusum, Kth. 
If a stem of this plant be cut through at the middle of the 
internodes, and the lower extremity of the piece cut off be stuck 
in moist earth, as soon as the adventitious roots already formed 
—— 
in the bark begin to be developed, very similar but not quite 
identical alterations take place in the tissues contiguous to the 
two cut surfaces. The organic constituents dissolved in the 
evaporating nutritive fluid collect beneath the dried layer of 
cells which soon covers the fresh-cut surface on exposure to the 
atmosphere, and are partly assimilated by the cells of which the 
various tissues of the mature stem of Philodendron are composed, 
and partly coagulated and chemically altered in many ways 
within the cell-membrane by the air which penetrates into the 
wounded tissues. 
On the end dried in the air the stratum of cells saturated with 
nutritive fluid, but completely desiccated, is considerably thicker 
than on the lower extremity, where it consists of one or a few 
layers of cells ; the vascular bundles also dry to a greater extent 
inwards than even the cellular tissue, so that a dead portion of 
these afterwards projects into the living tissue, and appears as 
if the latter had grown over it. 
Within the cells, rich in plasma, which lie next the withered 
layer, nuclear cells, containing nuclear corpuscles, make their 
appearance. These, however, do not acquire the size of the 
parent cells, but become displaced by two cells originating and 
