A preliminary account of the meiotic phenomena in the pollen mother-cells and tapetum of lettuce ( Lactuca sativa )

Abstract

On examining some lettuces which Prof. William Bateson, F.R.S., was growing in his experimental grounds at Merton, I was struck by the differences between a certain Cos lettuce (Sutton’s “Dwarf Perfection”) and a rogue from it which showed some resemblances in leaf characters to a cabbage lettuce. Prof. Bateson kindly permitted me to collect some cytological material of the variety and its rogue, and a subsequent study of the pollen development, particularly in the variety, has developed several points of so much general interest that a preliminary account of certain features was deemed desirable. So far as the work has progressed no constant difference between the variety and its rogue has yet appeared, the chromosome number being the same in both. The present account, so far as known, applies equally to the variety and the rogue. Only the main points of special interest in the meiotic history will be touched upon in this communication. The material was fixed in various chrom-acetic acid solutions, some of which gave very good fixation, and the sections were chiefly stained with Heidenhain’s iron-alum hæmatoxylin. In the resulting preparations the structural features both of the chromatin and the cytoplasm were beautifully clear, the presence of latex tubes causing no difficulties and requiring no special treatment.