Chromosomes in Osmunda

Shigéo Yamanouchi
1910 Botanical Gazette  
This paper presents the results of a study of the behavior of chromosomes during both homotypic and heterotypic mitoses in Osmunda cinnamomea L. The material was collected in the vicinity of Chicago, Illinois, in the late summer of i906 and the spring of i908. The study was made on both living and fixed material. Fixation was most satisfactory in Flemming's weak solution containing osmic acid. The chromosome conditions were studied not only in vegetative mitosis in sporophytes, and in
more » ... s, and in sporogenesis, but also in germinating spores and in mature prothallia. This paper, however, will be limited to a brief account of chromosomes in the sporophyte. Papers dealing with the cytology of Osmunda have been published by HUMPHREY (7), STRASBURGER (I5), SMITH (I4), FARMER and MOORE (2), and by GREGOIRE (4). These authors have all chosen Osmunda regalis. HUMPHREY and SMITH devoted their attention chiefly to the achromatic substance; STRASBURGER studied sporogenesis and the number of chromosomes; FARMER and MOORE claimed that the bivalent chromosomes arise by a folding of the spirem; and GREGOIRE studied chiefly the structure of the double spirem of synapsis, which he found to originate by the association of two independent chromatin threads. GREGOIRE'S account is in accord with the present study of Osmunda cinnamomea. The cytological investigation was carried on in the Hull Botanical Laboratory of the University of Chicago, under the direction of I This content downloaded from 071.I wish to express my sincere gratitude for their kind suggestions and criticism during the progress of the work. Description CHROMOSOMES IN TELOPHASE OF VEGETATIVE MITOSIS In order to make a detailed study of the behavior of the chromatin material throughout nuclear division, it is necessary to begin with the study at the earliest possible stage of division. To begin with the resting nucleus is not early enough, and so I have started at the telophase of the previous division. The nucleus in the vegetative tissue, whatever its location may be, presents similar features, so that the description can be applied to the process of nuclear division in any tissue, although the figures in the accompanying plate were drawn from vegetative mitosis in young fronds, previous to the formation of spore mother cells. The chromosomes in the equatorial plate in typical mitosis generally appear homogeneous. They split longitudinally and the two sets of daughter chromosomes begin to pass toward the poles. The slender and straight daughter chromosomes always retain this form until they reach the poles, where they are drawn more closely together and become more or less parallel. They remain for a while aggregated thus, in contact with the surrounding cytoplasm. If the chromosomes in this state could be called a nuclear primordium, evidently the daughter nucleus in the telophase consists of chromatin only. Then the process of vacuolation begins as follows. The loosely aggregated chromosomes draw near together and come into closer contact; at the same time each gradually loses its hitherto compact structure and vacuolation occurs irregularly at different places (fig. i) . The set of daughter chromosomes is thus a mere aggregate of vacuolate chromosomes. The limits of the individual chromosomes are not difficult to trace. The vacuolation seems to mean that there is either a secretion of fluid from the chromosomes or a dissolution of portions of them into liquid; and the contact of this fluid with the surrounding cytoplasm may precipitate a membrane which will separate the products of the vacuolate chromatin from the cytoplasm. The daughter nucleus formed in this
doi:10.1086/330085 fatcat:jzeckbsqa5bqdkmlzkrqdpwhvq