272 Prof. H. Karstea on the Formation, 



species of (Edogonium which will hereafter be described. This 

 may explain why Mohl and Sanio did not observe it, and why I 

 only succeeded a few times in meeting with stages of develop- 

 ment corresponding with that shown in PI. V. fig. 8. 



The presence of a lamina of cork of some thickness retards, 

 on the one hand, the flow of nutritive juices and their concen- 

 tration by evaporation, and, on the other, restricts the action of 

 the atmosphere on the cells assimilating it ; the newly generated 

 cells then extend themselves more slowly, and even appear to 

 remain in a half-evolved condition ; at least, in the line of de- 

 marcation between the cork and the unchanged cells of the 

 tissue, some of the latter are occasionally noticed to contain 

 delicately walled cells and vesicles, which possess the chemical 

 constitution of cork, and present all the intermediate stages to 

 that of the completely developed periderm, as is shown in PI. V. 

 fig. 2 X, in the case of a thickened porous cell of the medullary 

 sheath, and, in fig. 5, in that of a vessel. 



The most recently developed peridermic cells behave like cellu- 

 lose with a solution of iodine and chloride of zinc, but soon lose 

 the property of becoming blue on the addition of iodine and 

 corrosive reagents, which property they indeed do riot possess in 

 the first period of development. Probably cell-nuclei occur in 

 all cork-cells during a certain stage of development ; and their 

 duration seems to depend on the quality of the nutritive fluid 

 absorbed by the cell-tissue, and on the chemical composition of 

 the plasma withi» the cells, as well as on the more or less im- 

 mediate access of atmospheric air. 



The first-formed cork-cells contiguous to the withered cell- 

 layer mostly remain simple, whilst those subsequently produced 

 contain a further generation of two or more new cells. In this 

 manner such a cork-cell becomes occupied by a complete cell- 

 tissue, the very delicate walls of which are in such close ap- 

 position that they leave no intercellular spaces between them, 

 and cannot be recognized as consisting of a double membrane. 



Some layers of these cork-cells in the immediate vicinity of 

 the cut surface, soon after their evolution, acquire stratified 

 thickenings of their secondary cells, which are penetrated by a 

 few pore-canals. 



On resolving the tissue containing the cork-cells into its sepa- 

 rate cells, by boiling it with nitric acid and chlorate of potash, 

 and on subjecting it to the action of ammonia, the cellulose 

 walls of the parenchyma become more or less greatly swollen, or 

 are entirely dissolved. In the latter case, the solution of am- 

 monia also acts upon the coherent groups of cork-cells derived 

 from the dissolved cells, and causes them to swell up, to assume 

 a spherical form, and to part asunder (figs. 14 & 15). In this 



