| Abstract: | During the transformation of the protective sheath of garlic from a fleshy scale into a tough skin, most cells of the outer epidermis undergo wall thickening by secondary deposition, yet among them, a few cell interspersed after the fashion of stematal distribution, remain unthickened at the early stage of development (Plate Ⅰ, Fig. 1). While the unthickened cell maintains its original shape and protoplasmic contents, the nucleus and cytoplasmic constituents in the thickening cell begin to disassemble themselves to some extent and “nuclear extrusion” from one cell into the other (Plate Ⅰ, Fig. 2) can frequently be detected under microscope after the specimen is treated with a nuclear stain (Plate Ⅰ, Fig. 3). During middle stage of senescence cytochemical localization of several enzyme activities in the thickening and the unthickened cells (Plate Ⅰ, Fig. 5–8) have revealed striking contrast between the two kinds of cells: The unthickened cell is rich in ATPase (as well as in cytochrome oxidase and peroxidase) activity; whereas the thickening cell fails to show any. Conversely, the thickening cell is full of APase (and in polyphenol oxidase) activity but the unthickened cell shows none or very weak. Nevertheless, the conspicuous differences of the two kinds of cells do not last long the unthickened cell also transforms itself into the thickening one in succession at the late stage of senescence. Finally, the unthickened cell is composed of secondary deposition of wall materials and a narrow empty cell cavity (Plate Ⅰ, Fig. 4). Prominent differences in cellular structure and in enzymic activity at middle stage and their final trans- formation into the same rind structure toward the end of senescence seem to indicate that the unthickened cell is reserved to collect a large part of the evacuating cellular contents from adjoining thickening cells and to transpose them to the tissue underneath epidermis, hence the name “post cell” is given. |
