MORPHOGENESIS OF THE SPORANGIUM OF COMATRICHA

GOODWIN, DONNA C. (State U. Iowa, Towa City.) Morphogenesis of the sporangium of Comatricha. Amer. Jour. Bot. 48(2): 148-154. Illus. 1961.-Three species of the myxomycete genus, Comatricha, were studied: Comatricha nigra, C. fimbriata, and C. elegans. The sporangia developed on living bark of Ulmus americana in moist chamber. The hypothallus is formed under the homogeneous protoplasmic mass of the sporangial initial. The fibrous threads of the hypothallus hend upward, lengthening at the apices to become the fihers of the stalk and columella. The undifferentiated protoplasm is carried upward as the stalk elongates. When the columella has attained its mature height, threads bend out from the columella and grow toward the periphery of the sporangium. These threads form the capillitium. Simultaneous with the appearance of the capillitial initials, the peridium, a delicate membrane, forms. After the capillitium is mature, the protoplast cleaves into many cells, the future spores. The peridium evanesces early in the stage of spore maturation. Cellulose is present in the stalk, capillitium, and spore walls but is not found in the peridium or hypothallus. The capillitium of these species follows a developmental pattern designated as the "Comatricha-type" by Ross (1957) from a study of Comatricha typhoides. The taxonomic implications of the sporangial developmental pattern are discussed. THE MYXOMYCETE genus, Comatricha, established in 1851 by Preuss, was defined in our present-day concept in 1875 by Rostafinski, Aho noted that in Comatricha the peripheral edge of the capillitial net is characteristically open; that is, the ultimnate branchlets are free and do not anastomose. This absence of a closed surface net distinguishes the members of this genus from Stemonitis, in which the capillitial branchlets fuse to form a complete reticulum at the periphery of the sporangium. Miss Lister (1925), in her discussion of the genus, states that Comatricha is an artificial taxon: that it differs from Lamproderma only by having a fugacious peridium and from Stemonitis only by the absence of a smooth surface net of capillitium and a less clustered habit of the sporan-ia. Macbride and Martin (1934) agree with Lister and describe the distinction between Stemonlitis and Comatricha as " admittedly artificial" and "arbitrary." However, they add that, although the genera come close together, the artificial separation proposed by Rostafinski is convenient enough to justify retaining the 2 groups. Martin (1949) continues to use the presence or aI^sence of the surface net as a basis for distinguishing Cornatricha and Stemonitis. Results obtained from a recent morphological study by Ross (1957) on capillitial formation in 4 species of Stemonitis and in Comatricha typhoides have been 1 Received for publication June 12, 1960. Portion of a thesis submitted to the Graduate College of the State University of Iowa in partial fulfillment of the requirements for the decree of Master of Science. The author gratefully acknowledges the guidance and criticism of Professor C. J. Alexopoulos, and thanks him for taking the photographs which accompany this paper. She also thanks Dr. H. L. Dean who aided in the selection of chemical tests. 2 This research constitutes a part of a program "Experimental Approach to the Taxonomy of Myxomycetes," supported by National Science Foundation Grant G-6382. interpreted by him to indicate that the morphological development of the capillitium of the 2 genera differs. He designates a "Comatricha-type" and a "Stemnonitis-type" of development; in the former, the net originates as lateral extensions of tubes bending out from the columella, and in the latter the capillitium is derived from tubes forming in the peripheral protoplasm; these tubes grow inward from the periphery and outward from the columella and anastomose. In addition to his discussion on capillitium development, Ross describes, in detail, the formation of other sporangial structures of C. typhoides. Prior to Ross' paper, very little had been published on sporangial development in Comatricha or closely related forms. DeBary (1884) writes that the formation of sporangia of Stemonitis and allied forms differs from that of all other known Myxomycetes. He describes the growth of a hollow cylindrical tube in the interior of the protoplasmic mass and states that the primary capillitial branches arise from the outer surface of the columella. From his observations on Stemonitis fusca, Bisby (1914) concludes that hollow capillitial threads are formned by protoplasmic deposition in tubular capillary spaces produced by invaginations of the peridium. Lister (1925) states that the Stemonitaceae are characterized by a solid stalk which develops internally in the young rising sporangium. She mentions that the peridium is evanescent in Comatricha. In an exceedingly complicated discussion, Jahn (1931) notes that in C. nigra the stalk is deposited in the interior of the protoplasm and consists of individual solid fibers which are surrounded by membranes. The threads themselves he believes to originate through the thickening and infolding of membranes. Accompanying the text are a series of excellent photographs which depict the development