The Gametophore and Sporophyte of Mittenia plumula (Mitt.) Lindb

Abstract

An account is given of the gametophore and sporophyte of Mittenia plumula, stressing those features which have not previously been described.

The moss has a highly refractive lenticular protonema. There is variation in the arrangement of leaves on sterile and fertile shoots, a shoot may develop one or more side shoots at its base, and hairs are present in the axils of leaves. The capsule has a few small stomata at the base, and the inner peristome consists of 28-32 processes.

The double peristome of Mittenia plumula originates from three concentric layers of cells, the two innermost layers of the amphithecium and the outermost layer of the endothecium. In all other members of the Bryales whose examination has included early development, the peristome has been found to develop from amphithecial tissue only.

The 16 outer peristorno teeth are forined on the periclinwl walls separating the two outer peristome layers, thickening being laid down on the inner walls of the outer layer, which is composed of 16 cells, and in adjoining posit'ions on tho outor walls of the middle layer, which is composed of eight cells.

The inner peristome processes are formed on the periclinal walls separating the middle from the inner peristome layer (the latter being endothecial in origin). Thickening is laid down on the inner walls of the middle layer at positions contiguous with the junctions of the anticlinal walls of the inner layer, which is composed of 24-28 cells. Extra processes usually develop where the anticlinal wall is part of the original quadrant wall of the embryo. A smaller amount of thickening is then contributed to the processes from the inner peristome layer.

Variations in the development of the inner peristome are discussed, and a comparison is made with development of the double peristome of other members of the Diplolepideae.