. Essentials of botany. Botany; Botany. 222 ESSENTIALS OF BOTANY. 282. Discussion. — Spirogyra resembles Oscillatoria in consisting of filaments composed of a row of cells each of which is an individual plant. Its structure is, however, of a much higher character since the chlorophyll-containing material is in distinct bands, the pyrenoids form a special starch-making apparatus, and there is a well-defined nucleus. Spirogyra has a sexual as well as a non-sexual mode of repro- duction, while in Oscillatoria the reproduction is always non- sexual. Asexual reproduction, in Spirogyra as in Oscilla
. Essentials of botany. Botany; Botany. 222 ESSENTIALS OF BOTANY. 282. Discussion. — Spirogyra resembles Oscillatoria in consisting of filaments composed of a row of cells each of which is an individual plant. Its structure is, however, of a much higher character since the chlorophyll-containing material is in distinct bands, the pyrenoids form a special starch-making apparatus, and there is a well-defined nucleus. Spirogyra has a sexual as well as a non-sexual mode of repro- duction, while in Oscillatoria the reproduction is always non- sexual. Asexual reproduction, in Spirogyra as in Oscillatoria, con- sists of a process of cell-division, shown in Fig. 156. The nu- cleus divides into two daughter nuclei, and the protoplast be- comes divided into two portions. A new partition-wall begins as a sort of ring, or diaphragm, and at length completely separates the two new nuclei. The pro- cess of cell-division in Spirogyra is much more complicated than in Oscillatoria, as in the former plant the nucleus goes through a remarkable series of changes (mitosis) ^ previous to the formation of the daughter nuclei shown in Fig. 156. Sexual reproduction consists in the union of two appar- ently similar cells belonging usually to different filaments. A sexual cell which unites its contents with those of Fia. 156. Process of Non- Sexual Reproduction in a Spe- cies of Spirogyra. (x 230.) At n, n the daughter nuclei are seen on either side of tlie newly forming partition wall w. By its growth the partition pushes inward the band of chlorophyll c7i which lines the cell-wall. Sections of this band are seen at various points s. Threads of protoplasm join it to the nuclei. ^ See Bergen and Davis' Principles of Botany, Sect. 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 Bergen, Joseph Y. (Joseph Young), 1851-
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