A REINVESTIGATION OF CHROMOSOME COILING IN TRILLIUM

Abstract

THIS STUDY of chromosome coiling in Trillium was undertaken in the hope of resolving some disputed points in this material such as the presence of a minor coil and the time and manner of origin of the various coils. In the present paper, the terminology of Huskins (1941) has been adopted. The discovery by Fujii (1926) that the large gyred coils of the first meiotic division of Tradescantia are made up of small gyres of a second coil, whose longitudinal axis lies perpendicular to that of the large coil, was confirmed by Kuwada (1932), Kato (1935), Oura (1936) and others. Kuwada and Nakamura (1935) reported a major and a minor coil in the second division of meiosis in Tradescantia but it is generally agreed by investigators that there is only one coil in the second division, and that this one arises from the minor coil of the first division. Swanson (1942a) made a comparison between the coiling process as it occurs in Tradescantia and in Trillium using the findings of Huskins (1941), Huskins and Smith (1935), Wilson and Huskins (1939), Sparrow et al. (1941) and Coleman and Hillary (1941) as well as his own observations. From his investigation of Tradescantia, Swanson (1942a and 1942b) advanced the theory that the phenomenon of coiling is a process of initial spiralization followed closely by a prolonged despiralization. Evidence for this theory was found in the progressive decrease in number and increase in diameter of the gyres of the coils and the shortening of the chromosomes as meiosis proceeds in Tradescantia. These phases of spiralization and despiralization were at first not applied to Trillium by Swanson since little change was observed throughout meiosis in the number of gyres or in the diameter of the coils once they were formed. Later (1942b) Swanson stated that the theory can be applied to Trillium also but that the process of despiralization is interrupted or suspended in Trillium from late diakinesis to telophase II. A major and a minor coil, with little change in the number of gyres or their diameter, were found in the second meiotic division of Lilium by Kato (1935) and Iwata (1935), in Sagittaria by Shinke (1934) and in Trillium by Coleman and Hillary (1941). On the other hand, Huskins and Smith (1935) found in Trillium only a major coil that was stable throughout the stages of meiosis with nothing more than a waviness along the turns of the major coil. Warmke (1937) found no evidence of a minor coil in his study of the Pacific Coast Trilliums.