Histological studies on pollen degeneration in male-sterile Japanese radish.

(1) Previously the author (1951) reported on the spontaneous occurrence of the male-sterility in Japanese radish (Raphanus sativeis L.) and also explained that it was caused by a Mendelian reccssive gene. Results of histological observations carried out with anthers of both the sterile and its comparable fertile individuals are reported in this present paper. Flower buds or anthers were fixed with Carnoy's fluid. Usual methods of dehydrating and embedding in paraffin were employed. Sections were cut 10, h thick and stained with Heidenhain's iron-alum haematoxylin. (2) Development of the anther and formation of the pollen grains in the normal fertile radish : Tissues of a very young, anther consist of two parts, i.e., archesporial and parietal tissues. Archesporium situated in the center is surrounded by three or four layers of parietai cells. Cells of the former tissue are somewhat larger and rounder, and stained more densely with haematoxylin than those of the latter (Fig. 1). With the progress of auther development one layer of tapetal cells differentiates in the innermost part of the parietal tissues, enclosing the archesporium. Tapetal cells are clearly larger and angular or rather irregular in shape, and appear densely stained with haematoxylin than those of other neighboring tissues (Figs. 2 and 3). Such normal tapetal tissue begins, in turn, to degenerate when the pollen grains are formed, and it even disappears completely before the blooming time. On the other hand, the endothecium of the parietal tissue becomes thick and fibrous, so it can play an important rale for the dehiscence of anther walls (Fig. 4). Microsporgenesis proceeds quite normally and the mature pollen grains are seen well dispersed at the flowering.