Capsule Expansion in the Hairy-Cap Moss, Polytrichum

Abstract

In cultured explants of Polytrichum sporophytes, capsule expan- sion requires light. Red light is more effective in promoting expansion than white, blue, or green light of equal energy. The increase in capsule dry weight is a linear function of the length of the explant in the absence of dextrose for all lengths tested, and also in the presence of dextrose over the range 10-40 mm. In the absence of dextrose, capsule gain is a linear function of weight loss in the seta over the range in seta lengths 10-40 mm. With dextrose present, capsule gain has a nonlinear relationship to seta loss because dextrose suppresses seta loss relatively more than it enhances capsule gain, with increasing length of the explant. Polytrichum juniperinum Hedw. and P. ohioense Ren. & Card. were used in this study. Gametophytes and attached sporophytes were collected as turves during the winter and spring from Portland Arch, Indiana. All sporophytes were unexpanded, and each experiment is based on sporophytes of one age, only. The plants were freshly collected and grown in a greenhouse for a few days before each experiment, to condition them to the warmer temperature of the laboratory. At the start of an experiment, sporophytes were stripped of their calyptras and removed from the gametophytes, surface sterilized in 5% Clorox for 5 minutes, cut to length by removing the foot and a variable portion of the seta above the foot, and planted base down. Except where noted, explants were cut to 10 mm long. The length of the unexpanded capsule was estimated at 2 mm. The medium consisted of Voth's (1943) solution #5 solidified with 1% Difco Bacto Agar, with or without 1% dextrose. The explants were grown, one per 25 x 100 mm culture tube, for two weeks or longer at 23?C. Given an appropriate light regime, plants treated this way form