STUDIES OF PALEOZOIC FERNS: THE FROND OF ANKYROPTERIS GLABRA

PANKRATZ, H. S., and C. C. BOWEN. (Iowa State U., Ames.) Cytology of blue-green algae. I. The cells of Symploca muscorum. Amer. Jour. Bot. 50(4): 387-399. Illus. 1963.-The cellular morphology of Symploca muscorum is described, based upon electron micrographs utilizing improved techniques of specimen preparation. Except for a limiting plasma membrane, ribosomes, and Feulgen-positive chromatin, the cells have little resemblance to those of higher organisms. The longitudinal components of the cellular envelope consist of a 200-300 mIn fibrous sheath and a complex inner investment about 35 myA thick which includes at least 3 distinctly layered wall elements in addition to the typical 7-m,u unit membrane forming the plasma membrane. A row of very small elongate "pores" pierce the inner investment on each side of, and immediately adjacent to, the junction of the longitudinal walls and the crosswalls. Crosswalls vary in thickness from 3 to 20 m,u depending upon their age, and arise as elaborations of the inner layers of the longitudinal inner investment. The photosynthetic lamellar component of the cytoplasm consists of flattened sacs formed from unit membranes. The lamellae are concentrated in the peripheral region of the cell and usually are parallel to the longitudinal wall. These often extend from one crosswall to the next but, except for a few cases, are not continuous with the plasma membrane at either end. The Feulgen-positive nucleoplasm appears as an anastomosing system of lightstaining regions containing fibrils 2-5 m,u in diameter. The morphology and interrelationship of a number of other cellular elements are described: (1) structured granules range up to 0.5,u in diameter and occur near crosswalls; (2) polyhedral bodies, 0.2-0.5/s in diameter, are closely associated with the nucleoplasm; (3) "cylindrical bodies" characteristically consist of 2 concentric cylinders, are about 13 m,u in diameter and up to 1 , in length; (4) "a granules" are spherical or somewhat elongate elements about 30 m,u in diameter and characteristically associated with the photosynthetic lamellae and structured granules; (5) ", granules" are spherical, highly osmiophilic granules which range from 30 to 90 mi, in diameter; (6) ribosomes, 10-15 m/s in diameter, are most numerous near the nucleoplasm; (7) plasmodesms penetrate the crosswalls between adjacent cells. The cells of this organism can best be described as being in a "steady state" of division, and there is no evidence of any kind of organized distribution of the nucleoplasm to daughter cells during the constant progress of cytokinesis. I Received for publication October 6, 1962. This paper is based on a thesis submitted by the senior author to the Graduate Faculty of Iowa State University in partial fulfillment of the requirements of the degree of Master of Science. This investigation was supported by research grant C-3982 from the National Institutes of Health, United States Public Health Service. STUDY of the Cyanophyceae has been stimulated by the increased resolution of the electron microscope and new developments in fixation and embedding techniques. Until recently, phy-cologists were limited by the low resolving power of the light microscope and the small size of these This content downloaded from 157.55.39.111 on Sat, 17 Sep 2016 05:02:46 UTC All use subject to http://about.jstor.org/terms