NUCLEAR DIVISIONS IN THE TAPETAL CELLS OF CERTAIN ANGIOSPERMS

Abstract

Conflicting statements are to be found in the literature concerning the nature of the nuclear divisions in the tapetal cells of angiosperm pollen sacs. A number of investigators have m-iade casual observations concerning these divisions in the plant witlh whiclh they were working; and in a few instances, notably by Tischler (I905), Bonnet (I9I2), and Mascre and Thomas (I930), detailed studies of the divisions of the tapetal nuclei have been made. The earlier workers reported fragmentation, or amitosis, as the typical method of nuclear division in the cells of the tapetum. Strasburger (I882), reexamining his preparations, found mitotic figures in the tapetal cells and concluded that the appearances formerly described by him as amitosis result from the fact that two daughter nuclei remain attached and finally come to lie in close contact. Tischler (1905) in a study of three species of Ribes reported that the first division of the tapetal nucleus is by mitosis and that any further division is by constriction or fragmentation. Bonnet (I9I2), after critically examining the tapetal cells of ten species of angiosperms, concluded that amitosis does not occur in the nuclei of the tapetal cells and that figures suggesting amitosis are due to mitotic irregularities and nuclear fusions. In one of the plants studied by Bonnet, Datura Stramnonium, O'Neal (I920) reported that the nuclei of the tapetum divide by fragmentation. Mascre and Thomas (I930) agree with Bonnet concerning the absence of amitosis, but find that the tapetal cells may again become uninucleate through nuclear fusions. The presence of typical mitoses in the tapetal cells of Buginivillaea glabra (Cooper, 1931) suggested an examination of other angiosperms with the idea of determining, if possible, the exact nature of these nuclear divisions. Material of 7 mnonocotyledons and 36 dicotyledons, representing in all 24 families, was collected and examined. With the exceptions of the preparations of Pereskia acutleata, which were furnished by Dr. R. I. Evans, and those of Liliunm canadense, Ranunculus fascicularis, Meniispermnum canadense, and Gossypiuns barbadense, which were loaned by Dr. E. L. Fisk, the material for this study was collected in the botanical greenhouses or about the campus of the University of Wisconsin. Flemming's medium solution was used as a