A Schedule for Chromosome Counts M Some Plants with Small Chromosomes

Abstract

A schedule is given which produced excellent results for somatic chromosome counts on some British species of Galium, These species present great difficulties owing to the small size of the chromosomes (ca. 1.5μ long), the large somatic numbers (up to 96) and the slenderness of the root tips. Special features of the schedule, which is the result of much experiment with various technics, are: fixation with Belling's Navashin type fixative, which was quite the best tried; the modification of Randolph's card mount method to overcome the difficulty of the small diameter of the root tips by mounting together a number from the same plant, so that they can be embedded and sectioned almost as easily as much larger root tips; staining with dilute (0.1%) crystal violet, the most critical stain used, after mordanting with 1% aqueous chromic acid to intensify the stain in the small chromosomes; and the addition of an extra stage of differentiation in absolute alcohol diluted with xylol to remove strands of stain, which are often left in the cytoplasm between the chromosomes, since clove oil, usually the last differentiating fluid used, differs from alcohol in removing crystal violet more rapidly from the chromosomes than from the cytoplasm. It is suggested that this schedule will be valuable in chromosome counts of other plants where similar difficulties arise.