Development, and Structure of the Vegetable Cell. 189 
The most simple explanation of these phenomena appears to 
me to be, not that the cuticular layer is more or less completely 
regenerated according as the joint-cells are more or less well 
supplied with nourishment, but rather that it assimilates the 
nutritive material present, which reaches it both from without 
and from within, and transfers this to the inner cells, or, if this 
nutritive material be wanting, continues the function of nutri- 
tion at the expense of its own substance, and is finally destroyed 
by atrophy, whilst the neighbouring membrane of the joint-cells 
becomes unusually thickened. 
In like manner, also, the developing integumentary cell will 
probably, up to its complete evolution, possess the faculty of 
assimilating the nutritive fluids by which it is soaked, until at 
length, earlier or later according to its specific nature, it serves 
the assimilating inner tissue as nutritive material, even if this 
be only as a product of oxidation. 
Phases of development similar to those of the cuticle have to 
be passed through by the different membranes and membranous 
laminze of each individual cell-system of which the cellular tissue 
is composed ; the product of the liquefaction of the outermost 
comes at length to serve as nutritive material for the inner ones 
which are still living, or for those in course of development in 
other regions of the organism. 
As we know that the cellulose membrane formed by the meta- 
morphosis of the earliest, probably nitrogenous, cell-membrane 
changes by continual interchange of matter not only into lig- 
nine, xylogen, cork-substance, resin, and wax, but also into bas- 
sorine, gum, mucilage, and sugar, the notion that the formation 
of cellulose is the object and result of the interchange of matter 
in the vegetable cell must be modified as follows :—Many, in- 
deed perhaps most, vegetable cells have to pass through this 
chemical constitution of their membrane as a necessary phase of 
their development (a phase, however, which has scarcely been 
attained or exceeded by many of them when the organism to 
which they belong has already completed its cycle of life); but 
in many cases the cellulose cell-membrane employs the fluid by 
which it is permeated for still further changes of substance. 
With this are associated other instances, some of them com- 
municated in the preceding pages, of the independent growth 
of cell-membranes, and indeed of cellulose cell-membranes (as, 
for example, the peculiar fold-formation of the primary membrane 
of the joint-cell of Gdogonium, p. 285, vol. xii., Pl. VIL. fig. 49), 
which are opposed to the notion of the excretion of one cell- 
membrane by the adjacent ones. 
And not only does the membrane of the primary cell undergo 
chemical metamorphosis and accomplish peculiar changes of 
