Some Evidences for the Interaction of Tapetal and Sporogenous Cells in Certain Vascular Plants

Abstract

1. An interaction between tapetal and sporogenous cells in vascular plants is suggested. 2. Tapetal phenomena in normal sporangia are well known to be the following: (a) incomplete nuclear and cell division; (b) formation of polyploid nuclei; (c) formation of binucleate and quadrinucleate cells; (d) decrease in the cytoplasmic contents of the cells; and (e) digestion of tapetal cells as a result of enzymatic activity of sporogenous cells. 3. The above phenomena also occur under certain conditions in the sporogenous cells. The behavior of these cells, it is suggested, may result from the activity of tapetal enzymes. The changes which occur in the tapetum under these conditions are as follows: (a) an increase in the mitotic activity and in the period of time during which cell division may occur; (b) formation of two layers of cells; (c) an increase in the size of cells and in the density of their cytoplasmic contents; and (d) a decrease in the number of incomplete mitoses, and hence a decrease in the number of polyploid nuclei. 4. The sporogenous cells are affected in two ways: (a) they may be partially or completely digested, and hence, at maturity, the sporangium may contain only a few spores or no spores at all, and (b) interruptions of the mitotic activity resulting from the activity of an enzyme or enzymes produced by the tapetal cells may lead to incomplete mitotic division and a consequent doubling of the chromosome number. These cells may undergo meiosis and produce normal spores, as in some of the apogamous ferns. 5. It is impossible at present to state with certainty the conditions under which the behavior of the sporogenous cells simulates that of the tapetal cells. Experimental evidence may, perhaps, be necessary to account for the behavior of the cells in the sporangia of certain vascular plants. 6. If there is an interaction between tapetal and sporogenous cells, as is suggested, it is possible to account partially for the sterility reported in some pteridophytes, especially some of the ferns, and in a number of seed plants.