An einer bastimmten Stelle eines der langen Chromosomen bleibt die Paarung in alien Entwicklungsstadien regelmäßg aus. Dadurch gelang es, das eine Ende desselben Chromosoms zu markieren und im Laufe der Riesenchromosomenentwicklung die Zahi der Spiralwindungen, der Blöckchen und der sekundären Querscheiben an dieser Region festzustellen.
By means of the agar plate method, the action of p-acetylaminotropolone on mitosis was investigated in Tradescantia cells in vivo. In a concentration of 0.00005 and 0.000005 mol. solutions of p-acetylaminotropolone, mitoses occur de novo, which show chromosome bridges as well as chromosome fragments, when they enter into telophase. In higher concentrations than the above mentioned, several kinds of abnormal mitoses appear necrobiotically; or the occurrence of de novo mitoses is suppressed. In the Tradescantia test in vivo, two kinds of chromosome fragments are found; the occurrence of the first is confined to the resting stage or to the early prophase; this may be caused by the action of p-acetylaminotropolone. The occurrence of the second is in telophase and is caused by the refragmentation of the primary fragments, which are torn off by the developing cell plate or by the developing daughter nuclear membrane. From the standpoint of cell biology, the alteration of mitotic cell contents due to the change of concentration of chemicals; and the biological significance of the abnormalities of the mitosis which may appear in fixed preparations and in the necrobiotic as well as in the living state of the cell were discussed.
The two calendrid weevils, Sitophilus granaries and S. oryzae, have the chromosome formulae 11AA+Xyp and 10AA+neo-XY. They therefore differ from related Curculionidae, bisexual species of which, with the exception of Anthonomus scutellatus, conform to the formula 10AA+Xyp or 10AA+XO. Contrary to earlier reports they are nevertheless meiotically orthodox. Additional species investigated, with their formulae, are as follows: Platystomidae-Euparius marmoreus=10AA+Xyp; Curculionidae-Sitona lepidus, Sitona cylindricollis, and Hylobius congener=10AA+Xyp and Anthonomus scutellatus=13AA+Xyp; and Scolytidae-Hylurgops pinifex, Dendroctonus engelmanni, and Ips pini=14AA+Xyp. These findings are discussed in relation to the taxonomic disposition of the three families.
1. The cytological effects of the anti-f ungal antibiotic, Acti-dione, are presented and discussed. 2. Comparative studies of fifteen minute exposures and continuous exposure to concentrations ranging from 1 to 80ppm have been made. 3. An attempt has been made to assay quantitatively the effects of Acti-dione on frequency of mitosis, relative frequencies of different stages of mitosis and rate of increase of aberrations. 4. In general the effects of Acti-dione are similar to those of salts of nucleic acid and superficially similar to those of colchicine. 5. Some treatments show a significant increase in the frequency of various types of “reductional” and “segregational” figures.
In unfixed tissues of the nucleolar wall of L. campestris, the nucleoli are occasionally bipartite or U-shaped, When bipartite, their appearance may be similar to that of heterochromatic elements visible in smear preparations. When treated with acetic acid, the atypical nucleoli react similarly to normal nucleoli and unlike the chromosomal substance. The atypical nucleoli are usually not stained by the custamary aceto-carmine technique but can be stained intensely following Rattenbury's formol modification. Atypical nucleoli are much more frequent in nuclei with two nucleoli than would be expected if their occurrence were not related to the binucleolate condition. The idea is offered that the atypical nucleoli are formed in part by a failure of the usual fusions of material collected by the organizers. A further observation of vacuoles in unfixed nucleoli is noted.