The nucleolus of tmesipteris tannensis , bernh

Abstract

In some slides from young synangia of Tmesipteris , prepared from curiosity regarding this unique plant, it was noticed that during mitosis there were present, in addition to the chromosomes, several rounded bodies similar to the nucleoli of resting cells. Moreover, nucleoli were present in nuclei where the spireme was fully developed prior to mitosis. Preliminary examination thus suggested Tmesipteris as a most favourable plant for a study of the nucleolus as regards its relationship to the chromosomes and its behaviour during mitosis. Historical . The study of plant-nucleoli has been largely incidental to the investigation of chromosome behaviour, more especially during the meiotic divisions. The general conclusions from the study of plant-nucleoli may be summarised thus:— The number of nucleoli per cell may vary from one up to eight or ten, some of which may arise by the division of pre-existing ones. (1) In some cases they have been regarded as stores of material which contribute to the building of the chromosomes in prophase (2, 3), while in other cases this, explanation has been rejected. Another view, supported by Strasburger and Chamberlain (4, 5) amongst others, is that spindle-formation is a function of the nucleoli. Others again hold that extruded portions of the nucleolus are converted into organs such as the blepharoplast of Hepaticœ . Extrusion of chromidia into the cytoplasm by nucleoli has been described by various cytologists (6, 7), and Digby (1) finds that the nucleolus of Galtonia is closely related to one pair of chromosomes, and at metaphase is “pushed” away from the equatorial plate on the end of a chromosome. Lack of genetic continuity between nucleoli has been advocated by many authors, especially by Gates (8, 9, 10) and by Mottier (11).