The Number and Morphology of Moss Chromosomes

The time that suitable cytological material is available can be extended by bringing mosses into the laboratory in late winter and keeping them in covered glass dishes placed in strong diffuse light. Best growth of the gametophyte occurs at 68-70° F. and at a relative humidity just high enough to prevent the leaves from curling. Fruiting plants can be maintained in the laboratory in the same way but at a slightly lower relative humidity. Tissue for the study of the gametophytic chromosome complement is obtained from the stem apex and embryonic leaves. Sporophytic mitoses are obtained from the meristematic tip of developing sporophytes. For the study of meiosis, the columella, to which the spore mother cells adhere, is removed from the capsule. The tissues are fixed in acetic alcohol for 1-3 hours and then stained and squashed. Ways in which moss tissue reacts differently to the conventional squash methods are discussed and special directions are given.