270 Prof. H. Karsten on the Formation, 



The statement given by me as 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 lamina 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 



