Development of the Ovule and Megagametophyte in Saxifraga Hieracifolia

Abstract

WIGGINS, IRA 1. (Stanford U., Stanford, Calif.) Development of the ovule and megagameto· phyte in Saxifraga hieracifolia. Amer, Jour. Bot. 46(10) : 692-697. Illus. 1059.-Buds of Saxifraga hieracijolia collected in the vicinity of Point Barrow, Alaska, fixed, sectioned, and stained by standard methods, revealed that the archesporial cell in the ovule of this species is hypodermal and gives rise to the megaspore mother cell and a small number of parietal cells. Occasionally 2 megaspore mother cells occur within an ovule. Meiosis in the megaspore mother cell produces a linear tetrad of megaspores, the chalazal one of which normally gives rise to a monosporic, Polygonumtype megagametophyte. The polar nuclei fuse near the chalazal end of the megagametophyte and the antipodal cells disintegrate prior to fertilization. A distinct filiform apparatus and a marked lateral "spur" develop on each synergid. Vacuolation in the egg cell and in the synergids follows the usual pattern. Only a single integument surrounds the nucellus.

Embryological Studies in the Family Saxifragaceae (S.L.). I. Development of the Ovule and Embryo Sac in Saxifraga Fortunei Var. Partita (Makino) Nakai

“…crassifolia, by Schiirhoff (1925) in S. decipiens x granulata, by Chapman (1933) in S. virginiensis, by Harmsen (1939) in S. stellaris var. comosa, by Wiggins (1959) in S. hieracifolia and by Saxena (1964a) in S. diversifolia. In addition, there are some papers in which development is described incompletely.…”

“…In the genus Saxifraga, the most representative herbaceous genus of this family, however, both unitegmic and bitegmic conditions have been reported. Chapman (1933), Harmsen (1939), and Wiggins (1959) reported the occurrence of the unitegmic ovules in Saxifraga virginiensis, S. stellaris, and S. hieracifolia, respectively, while Juel (1907) and Saxena (1964a) reported that the ovules of S. granulata and S. diversifolia had two integuments, and, judging from the figures in Pace (1912), S. ligulata and S. crassifolia also have bitegmic ovules, though not clearly mentioned in the manuscript. Chapman (1933) and Harmsen (1939) did not discuss the relationships between bitegmic and unitegmic conditions within the genus Saxifraga.…”

“…Chapman (1933) and Harmsen (1939) did not discuss the relationships between bitegmic and unitegmic conditions within the genus Saxifraga. Wiggins (1959) referred briefly to this problem and suggested that the unitegmic condition of S. hieracifolia could not be derived by the elimination of one of two integuments. The single integument of S. stellaris var.…”

“…comosa [Vol. 69 had 3-4 layers (Harmsen, 1939) and that of S. hieracifolia also seems to have 3-4 layers, though not described in the text (Wiggins, 1959). Since both integuments are mostly twolayered in the bitegmic saxifrages, the unitegmic condition of some saxifrages may be caused by fusion of the two integuments.…”

“…The occurrence of the indentations of the mature synergid cells are also rather rare in this genus. Only two cases are clearly illustrated, i.e., in S. cordifolia (Pace, 1912)and in S. hieracifolia (Wiggins, 1959).…”