ON THE OCCURRENCE OF INTERCELLULAR PECTIC WARTS IN COMPOSITAE

Abstract

IN A NUMBER of vascular plants, protuberances of various shapes characteristically occur on the outer surface of parenchyma cell-walls facing intercellular spaces. As the review of Kisser (1928) shows, these structures have been demonstrated in stem, petiole, or lamina of various ferns and of a small number of Equisetaceae, Cycadaceae, Taxaceae, and Angiospermae. They have been found also in aerial roots of orchids (Noack, 1892) and palms (Jost, 1887) and in the seed coats of Leguminosae (Mattirolo and Buscalioni, 1889). Kisser (1928) was unable to find any of these structures, which he terms Pektinwarzen on account of their chemical composition, in the Compositae he investigated. During a survey of the anatomy of the genus Fitchia and other members of the tribe Heliantheae (Compositae), the writer encountered such pectic warts in certain tissues of Fitchia speciosa Cheeseman and Wyethia ovata T. & G. Because these pectic warts represent a new record and differ in several respects from those described by Kisser and others, a description of these, together with photomicrographs-seemingly the first published of pectic warts-appeared desirable. Although inconspicuous and perhaps rare in vascular plants, intercellular pectic warts represent a neglected phenomenon which requires explanation by students of cell wall structure. MATERIALS AND METHODS.-Vegetative material of Fitchia speciosa (Carlquist H293.), was fixed in a Carnoy's fluid (3 parts absolute ethyl alcohol: 1 part glacial acetic acid). Material of Wyethia ovata (Carlquist 398 3), was fixed in formalin-propionic-alcohol (Johansen, 1940, p. 42). For infiltration and embedding of both species, the tertiary butyl alcohol series of Johansen (1940, p. 130) was used. The sections of Fitchia speciosa (fig. 1-4) were stained by the tannic acid-ferric chloride schedule of Foster (1934). For sections of Wyethia ovata, a safranin-fast-green combination corresponding to Northen's modification of Foster's tannic acid-ferric chloride method (Johansen, 1940, p. 92) was employed. Although the dehydration entailed by the above microtechnical methods tends to shrink structures rich in pectic materials, comparison of fresh material with paraffin sections of Wyethia ovata revealed no appreciable differences. It seems likely that the swelling tendency of the weak acids employed in fixation may have compensated for the shrinking effect of