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).

PHENOMENA OF HETEROTYPIC DIVISION IN THE POLLEN MOTHER‐CELLS OF A TETRAPLOID FORM OF RUMEX SCUTATUS VAR. TYPICUS*

“…Its position inside the nucleus does not signify anything more than its being exclusively related to the nucleus itself, or, in other words, that the nucleus is necessary for the formation of the nucleolus as much as a plastid is necessary for a starch grain. Yeates (1925) considers the nucleolus as a product of the metabolism of the chromosomes.…”

“…Again, there are cases in which these dark bodies appear to be not inside the vacuole but lying on the top of it. Yeates (1925) shows that the appearance of these bodies depends on the fixative used. After certain fixatives (corrosive sublimate, formalin and acid fixatives, except methyl green), the nucleoli appear homogeneous with occasional small vacuoles.…”

Studying the Transfer of Magnetic Helicity in Solar Active Regions with the Connectivity-based Helicity Flux Density Method

“…Magnetic helicity is hence at the heart of several MHD theories of coronal processes including, but not limited to, coronal heating through the relaxation of braided magnetic fields Electronic address: dalmasse@ucar.edu (e.g., Heyvaerts & Priest 1984;Russell et al 2015;Yeates et al 2015), the formation of filament channels through the inverse cascade of magnetic helicity (e.g., Antiochos 2013; Knizhnik et al 2015), the existence of CMEs as the mean for the Sun to expel its magnetic helicity excess (e.g., Rust 1994;Low 1996), and the production of very high-energy flares via magnetic helicity annihilation (Linton et al 2001;Kusano et al 2004). Recently, Pariat et al (2017) even showed that specific quantities derived from magnetic helicity have a strong potential for greatly improving the prediction of solar eruptions.…”

Annotated summaries of letters to colleagues by the New Zealand botanist Leonard Cockayne-2

“…However, he was also aware of the contributions cytology could make to taxonomy and to theories on evolution. Yeates (1925) in his study of the nucleolus of Tmesipteris acknowledges Cockayne " ... for help he has freely given ... ". In some personal reminiscences, Dr Yeates (pers.…”