The Ohio Naturalist And Journal Of Science Volumes Xiv Xv 1912 1915 PDF Download

Excerpt from The Ohio Naturalist and Journal of Science, Vol. 15: 1912-1915 He did not find a conjugation of two threads during synapsis. He mentions a slight resting stage between the first or heterotypic division and the second, homotypic division, but docs not speak of any longitudinal splitting of the heterotypic chromosomes until after the transverse splitting occurs. The longitudinal splitting was visible just before the chromosomes reached the poles. Gates (7) in his paper on Oenothera rubrinervis, states that the contraction of the chromatin material is synapsis and that since the cytoplasm of the cells shows no contraction, the cell is perfectly fixed. For this reason, the contraction, so constantly observed at an early stage in the process, is not an artifact, but is a real contraction stage, leading to synapsis. As this contraction proceeds the reticuim is re-arranged into a long, continuous delicate thread. No indication of a doubling or pairing of the threads was evident. After the synapsis the spiretn shortens and thickens and begins to arrange itself more loosely in the nuclear cavity. This shortening is progressive and continues for some time. He states that the shortening may be uniform, or it may vary or may be irregularly constricted at varying intervals. This thickened thread now segments transversely into fourteen chromosomes-fourteen being the sporophytic number. Then these chromosomes break up into pairs which later fuse with each other leaving the x numljcr of chromosomes. They arc taken on the spindle and reduction follows in the usual way. In his paper on Oenothera lata x O. gigas (9) he begins his dicussion with the telophase The usual number of chromosomes found in the hybrid is twenty-one, seven being of maternal and fourteen of paternal origin. In the reduction one germ cell receives ten and the other eleven chromosomes. In a few cases nine and twelve chromosomes were the numbers found at the respective poles. One cell was found which had twenty chromosomes, ten of which went to each pole. The segmentation into ten and eleven proves that there is not a pairing of homologus chromosomes of maternal and paternal origin but the segmentation tends to be into two numerically equal parts. Gates claims evidence from his work, that there are two general methods of chromosome reduction, one a side to side pairing of chromatin threads (parasynapsis) to form a double spirem; the other involving an end to end arrangement (telosynapsis) of maternal and paternal chromosomes, to form a single spirem which afterwards splits longitudinally. He says an individual always has as many chromosomes as the sum of the chromosomes in the germ cells which go to form the new plant. This fact, he says, supports the genetic continuity of the chromosomes. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.