Development, and Structure of the Vegetable Cell. 271 
growing with them in the juice of the cell, and either nucleated 
or non-nucleated according to the chemical constitution of the 
plasma, or are enclosed between these during their growth, and 
absorbed; at any rate, they disappear. 
The two newly formed and very thin-walled cells subdivide 
within’ the cavity of the mother cell, and so completely occupy 
it, and are so intimately moulded to its walls, its pores, rings, 
and spiral windings that they can scarcely be distinguished 
from its membranes. In the same way, the septum, which owes 
its origin to the apposition of the two daughter cells within the 
parent cell, is of such great tenuity as to appear hke a single 
lamella. 
The same new formation proceeds in the cells of the cortical 
tissue next the epidermic layer; and in this region the newly 
formed tissue extends from the cut surface almost as deeply 
within the cell-tissue as the dead portion of the vascular bundles. 
These newly formed pairs of cells are always arranged, in the 
upper section exposed to the air, in a direction perpendicular to 
the adjoming dry and air-containing cell-tissue, and more or less 
indeed in the same peculiar manner as the cork-cells of the bark, 
forming uninterrupted rows with the successively produced 
young cells. These are united in the parenchyma im a plane pa- 
rallel with the cut surface, and which, close to the epidermis and 
round the vascular bundles, is turned wards. By this means 
the surfaces of the dead extremities of the vascular bundles pro- 
jecting into the living parenchyma are invested by a sheath 
formed by a stratum of cell-series standing perpendicularly to 
their longitudinal axis. 
This production of cork-cells is moreover found not only in 
the cells of the parenchyma, but also in the cells and vessels of 
the vascular bundles; so that even the latter become occupied by 
a layer of cork-cells, and the undisturbed tissue of the internode 
is separated by this intimately adherent layer of cork-cells from 
the withered tissue, and also protected from the immediate in- 
fluence of the atmospheric air. 
The cork-cells do not always arise in pairs, but in larger 
number sometimes in cells of greater length. In the elongated 
cells of bast and wood, as well as in the vessels, there are usually 
numerous cells, arranged in rows, beginning at the end to- 
wards the cut surface, filling up the long cells more or less 
completely. In the vessels, moreover, they still oftener give 
origin to an irregular tissue. | 
The enlargement of the cells filled with transparent fluid, 
produced together with the cell-nucleus, must take place with 
extraordinary rapidity in the vicinity of the cut surface, in the 
manner that may be directly observed in the tissue-cells of a 
