Little has been contributed to our knowledge of the chromatophore and pyrenoids of Closterium since the time of NXGELI and DEBARY, though several investigators have worked on the cell division, conjugation, and peculiar mode of locomotion of these plants. NAGELI (5) described the chromatophore, nucleus, end vacuoles, pyrenoids, and cell wall of the genus. He figures only C. moniliferum and C. parvulurm, but mentions eleven other species as belonging to the genus, not including, however, C. Ehrenbergii among them. The chromatophore as described by him consists of three or more chlorophyll plates whose inner edges rest in the axis of the cell and whose outer edges extend to the cell wall. In optical cross section, obtained by examining the plant when it was standing on end, the chromatophore appeared to be made up of 3 to I5 plates extending radially from center to periphery. The nucleus he describes as a clear sac containing a denser body. In the colorless ends of the plant body are the clear vacuoles containing little black granules showing a motion which he calls molecular; these vacuoles are usually spherical, although at times irregular in shape. The pyrenoids, "little chlorophyll sacs," are arranged in C. moniliferum and C. parvulum in a single row of 2 to 20. The cell wall is striate. NXGELI'S figures show, besides the external views, optical cross sections of C. moniliferum and C. parvulum. These are the only figures extant and they have been copied by OLTMANNS (I7) and LOTSY (I2). DEBARY (5) also described Closterium, but adds little to NXGELI'S account except that he recognizes the pyrenoids (Amylonkerne) as 241 242 BOTANICAL GAZETTE [APRIL depositing starch in their interior, and made out that the little granules in the end vacuoles are rhombic plates with sharp angles, composed, as he discovered by tests, of gypsum. DEBARY used the term Amyloukerne for the pyrenoids because of the many analogies they offer to the cell nuclei. He had discovered by means of the iodin reaction that the outer layer is starch, and by means of the red coloration with sugar and sulfuric acid that the central body is composed of protein. He described the starch which appears in the outer layer as either forming a homogeneous shell on the outside of this central body, or in the cells rich in starch as composed of grains that give to the pyrenoid an irregularly cracked appearance. DEBARY was the first to give an adequate account of the appearance and chemical constitution of this body in Closterium, and little of real importance as to its chemical nature has been added since. FISCHER (7) examined the crystals in the end vacuoles both as to their origin and composition. In his opinion they originate in the plasma, in which he claims there are many of them, from which they wander into the vacuoles. LtTKEMtLLER (13) and a number of other observers have studied the structure and the beautiful and characteristic markings on the cell walls of the different species. Later authors, working on other forms, have found little to correct in ...
Historical The first figures showing division in desmids were those of Cosmarium by EHRENBERG (II). Those drawings, while not entirely accurate, indicate clearly that he saw the two new daughter half-cells being interpolated between the old ones. Each half of the parent cell was evidently considered by him as an individual, since his genus description states that the individuals are arranged in the colonies "in chains of two or four." NXGELI (33), RALFS (35), and FOCKE (I7) observed cell division in the desmids and gave fairly complete accounts of the process. DEBARY (g) did not describe division in detail, but mentions the fact that the newly formed transverse wall of Closterium and Penium is flat, and that the new end grows out as a cone-shaped structure. As the chromatophore is divided into two parts, some of the older observers, as EHRENBERG, regarded the mature plant as a chain of two cells, but DEBARY was clear on this point and recognized the desmid as a single cell with a nucleus between the halves. Nothing was observed by any of these investigators as to the conduct of the nucleus during division, as the importance of that organ of the cell was not yet fully recognized. It is to ALFRED FISCHER (14) that we owe our first knowledge of the details of the process as it occurs in this genus. FISCHER found the cross-wall formed in essentially the same manner that STRASBURGER had described for Spirogyra. It appears soon after 40I
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