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 

 laminae of each individual cell-system of which the cellular tissue 

 is composed ; tbe 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 necessarj' pbase 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 joiut-cell of (Edogonium, p. 285, vol. xiii., PI. VII. 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 



