On Mounting Delicate Bryophytes in Glycerol

Abstract

Glycerine jelly is an effective substitute microscopic mounting medium for now difficult-to-obtain gum chloral preparations. It does not collapse most thin bryophyte tissues, preserves color responses of cell walls to potassium hydroxide solution, and is made from easily obtained, non-poisonous ingredients. Like other glycerol-based mountants, it evaporates only very slowly and, with luting, is essentially permanent. The study slide is a valuable adjutant to research in bryology. A well labeled permanent or semi-permanent preparation allows repeated examination of morphological traits that allows serial comparisons during revisionary work and serves to reinforce poorly remembered distinctions or illuminate vaguely worded keys during routine identification. For critical species, I find two slides, each with two coverslip-protected mounts, provide space for mounting moss capsules, perichaetia, perigonia, habit (of smaller species), and sections of stem and leaves in a manner that allows subsequent illustration if needed. As anyone who has worked with microscopic mounts knows, taking the time to prepare a slide well saves much time and frustration in the long run. To this end, I have pursued (Zander 1982, 1983, 1993) a better slide medium than gum chloral preparations such as Hoyer's Solution (Anderson 1954), which have severe osmotic effects in many bryophyte species. In addition, chloral hydrate is presently governed under controlled-substance laws in the U.S.A. and good-quality powdered gum arabic is now difficult to obtain. Glycerine jelly has been used for many years as a bryological microslide mountant (Gatenby & Beams 1950; Gray 1954; Murray 1926) but has been superseded in bryological work to a great extent by Hoyer's Solution (Anderson 1954), which is more convenient to work with since it does not need to be heated. Hoyer's Solution and its variants are likewise made with glycerol, and thus last for many years since glycerol has a very low vapor pressure (boiling point 2900C). The high index of refraction of glycerol (much higher than that of cellulose), makes mounted tissue easy to observe un-