. The essentials of botany. Botany. REDUCTION OF CHROMOSOMES 111 sion does not enter in until the spores are being produced, which give rise to the sexual generation (gametophyte). This latter has the haploid number of chromosomes in its nuclei. We must thus distinguish carefully between typical asexual reproduction, where the resulting plant is, as it were, but a separated part of the mother plant, and the formation of a gametophytic generation from the spore produced in the sporophytic generation. In- deed each of these generations may have typical asexual reproduction leading simply to the
. The essentials of botany. Botany. REDUCTION OF CHROMOSOMES 111 sion does not enter in until the spores are being produced, which give rise to the sexual generation (gametophyte). This latter has the haploid number of chromosomes in its nuclei. We must thus distinguish carefully between typical asexual reproduction, where the resulting plant is, as it were, but a separated part of the mother plant, and the formation of a gametophytic generation from the spore produced in the sporophytic generation. In- deed each of these generations may have typical asexual reproduction leading simply to the formation of other plants of the same generation. 160. After the union of gametes the chromosomes from the two gametes remain separate, but usually the corresponding chromosomes from each gamete lie close together. In the reduction division the chromosomes gather at the equator of the spindle as double chromo- somes, in all probability representing the two corre- sponding chromosomes from the two gametes. Before this stage is reached, and while the chromatin matter is found on fine threads, there is a characteristic bunch- ing together of these threads (called the synapsis) in the course of which it is sup- posed that certain characters become ex- changed m the COrreS- j.^^, 49.—Reduction division (diagrammatic). ponding chromo- somes. These double chromosomes split apart and as single ones go to the opposite poles. There are thus entering into each daughter nucleus only as many chromo- somes as were originally present in the gametes. These. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bessey, Charles E. (Charles Edwin), 1845-1915; Bessey, Ernst Athearn, 1877-1957. joint author. New York, H. Holt and company
Size: 1912px × 1307px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublisher, booksubjectbotany
