GAMETOPHYTE DEVELOPMENT IN REBOULIA HEMISPHAERICA

Abstract

In so far as the writer is aware, a description of the germination of the spores of Reboulia hemisphaerica has not been published. Spores for this study were collected before the middle of May at Sag Ravine, Cook County, Illinois, and in the latter part of the month at Sinsinawa Mound, Grant County, Wisconsin. The spore output in Reboulia is very small as compared with Marchantia polymorpha (3). The number of capsules to a head ranges from one to five (5) and the average number of spores to a capsule is approximated at 2500. The spores of Reboulia have already been described by Haupt (2) and by Miss Blair (i). The results as here reported were obtained from two kinds of cultures, those in which the spores were sown on a mineral nutrient solution and those in which they were sown on porcelain plates kept moist with the same solution, a modification of Knop's mineral nutrient solution, in glass containers. All of the cultures were kept indoors in a room with north, south, and east exposures. Spores were thus germinated and young gametophytes developed in the spring, that is from a little after the middle of May until the middle of June, and from about the fifteenth of October until November fifteenth. There is little or no change in the size of the spores (P1. XLV, fig. I), 70 to 8o microns in diameter, subsequent to their being sown until germination occurs. In this respect, as also in the paucity of spores, Reboulia resembles Preissia (3) and is in sharp contrast with Marchantia polymorpha, in which the spores, relatively very numerous and exceedingly small, about i8 microns in diameter, increase in size to probably eight times their original volume before germination occurs. Spore germination is evident and, under favorable conditions of illumination and moisture, occurs in from two to five days. The spores seem to retain their viability for a considerable time as germination of spores about five and one half months old was probably one hundred percent. Spores a little older than these showed a low percentage of viability only, and germination tests made on spores seven to eight months old were totally negative. The first step in spore germination consists in the emergence of a germ tube with almost a simultaneous protrusion of a rhizoid more or less at right angles to the germ tube (figs. 2, 3). The nucleus, chloroplastids, and 765