XIII. On gasterolichenes: a new type of the group lichenes

Abstract

Until recently the time-honoured division of Thallogens into three primary groups, Algæ , Fungi , and Lichenes , was retained, the most prominent morphological features of the last group consisting in the vegetative portion being composed of slender achlorophyllose threads mixed with chlorophyll-producing cells or gonidia, and the spores produced in asci. It was assumed that the gonidia were in organic continuity with the colourless threads, an assumption challenged by Schwendener, who considers a lichen as a combination of a fungus and an alga, an idea now widely entertained, nevertheless, curiously enough, numbering amongst its opponents most of the leading lichenologists and mycologists of the day, most of whom, it is important to remember, are distinguished as systematists rather than as biologists. Later researches have placed almost beyond doubt the truth of Schwendener’s theory. Bornet has shown that in numerous instances the gonidia can with certainty be referred to some species of Algæ, and further succeeded in building up a lichen synthetically by sowing the spores of Parmelia parietina upon Protococcus . Stahl also, by growing the spores and gonidia ( pleurococcus ) of Endocarpon Pusillum , produced the lichen which bore perithecia and spermogonia. The same author has also demonstrated the presence of sexual organs of reproduction in a gelatinous lichen, Collema Microphyllum , the female portion resembling the carpogonium, with its trichogyne, met with in the Florideæ. Spermatia, produced in the spermogonia, are the fertilising elements. The discovery by Mattirolo of a second type of lichen structure, Hymenolichenes , characterised by having the spores borne on basidia, the latter compacted into a continuous hymenium as in Hymenomycetous fungi, has also considerably strengthened Schwendener’s theory, as the mutual relations between the two components can be more readily determined than in the older group of Ascolichenes .