Art. LIV.—Description of a new Lichen (Stereocaulon buchanani).
[Read before the Wellington Philosophical Society, 21s November, 1874.]
A Few days ago I received from Mr. J. Buchanan of the Colonial Museum, Wellington, a lichen which presents peculiarities of internal organization of sufficient importance to warrant a special notice. As these peculiarities are somewhat anomalous, the absence of spermogonia in the specimens is so far a matter of regret, inasmuch as its generic place is rendered to a certain extent doubtful.
Of late these secondary organs of fructification have been occupying considerable attention, and the modifications in size and shape of the spermatia, as well as the comformation and appearance of the spermogonia themselves, have served, in doubtful cases, as a means of discriminating genera, more especially Lecanora from Lecidea.
The lichen in question occupies an isolated position, and presents affinities to three genera, viz:—Gomphillus, Stereocaulon and Bœomyces.
In the extreme length and tenuity of its spores, the former dimension reaching almost the limit, in this respect, amongst lichens; in the tenacious stiff gelatine which prevades the hymenium, and almost conceals the paraphyses until the application of liq. potassæ, which softens if it does not dissolve this gelatine; as well as in the presence of longitudinal cavities apart from the thecæ, this lichen shows considerable affinities to the curious and anomalous genus Gomphillus. On the other hand the apothecia, in their external conformation and, more especially, in the fact that occasionally very short stipites are present, coated with granules, betray a manifest relationship to Stereocaulon, with which I have meanwhile united it. This relationship is brought out all the more through the variety of St. condensatum, Hffm., where the apothecia are found also sessile on mosses, and have at first sight much the aspect of those of a Lecidea.
During the current year I detected on Ben Lawers, Perthshire, a form of
[Footnote] * Dated at Glasgow, 21st September, 1874.
this variety of St. condensatum, where the apothecia do not betray the slightest traces of stipites, and which, in the absence of intermediate states, I am strongly inclined to elevate to the rank of a species, more especially as the spores are shorter and thicker than any belonging to this species hitherto seen.
In St. strictum, Bab., as well as in one or two others, are seen spores, very much resembling those of the present lichen, although not more than half their length. The reactions by means of iodine on the hymeneal gelatine also correspond generally to those seen in species of the same genus.
The relationship of this lichen to Bœomyces is less obvious, and, but for Dr. Nylander's assertion, (Synop. p. 175) and a certain primâ facie resemblance, I would not have mentioned this genus as analogous, indeed in the light of the present plant I can assert, with considerable confidence, that Gomphillus has much stronger affinities to Stereocaulon than to Bœomyces.
In plants such as the present it is extremely foolish to dogmatize in the matter of classification, and we are taught the lesson that nature is not to be cramped and confined by any such well defined limits as our modern classifiers would fain lead us to believe.
Stereocaulon buchanani, Strn.
Thallus tenuis effusus, cinerascens vel cinereo-virescens, e gonidiis conglomeratis mediocribus et filamentis irregularibus, fere omnino constans; apothecia majuscula (latit. 1—2 millim.), sessilia vel elevato-sessilia, interdum conglomerata, fusca (junioribus pallidis et nonnihil turbinatis), convexa et immarginata, intus fuscescentia, textura tenaci cornea. Sporœ 8næ, in thecis cylindricis, longissimæ, filiformes, 40–50-septatæ, longit. 0.16–0.22 millim., crassit. circa 0.003–0.004 millim.; paraphyses haud distinctæ. Gelatina hymenialis iodo leviter cærulescens (apicibus thecarum intensius tinctis) dein rufescens.
Thallus thin granular cinerascent or cinereo-virescent effuse, composed almost entirely of conglomerated gonidia of a medium size and an irregular fibrous stroma; apothecia rather above average sessile or elevato-sessile fuscous, in a younger state much paler and then somewhat turbinate, convex and immarginate, fuscescent within and of a tenacious horny texture; spores 8, in cylindrical asci, very long and filiform, 40–50-septate, and measuring 0.16–0.22 by 0.003–0.004 of a millim., paraphyses not distinct. Hymeneal gelatine slightly cærulescent with iodine, the apices of the asci more deeply tinted, the whole assuming afterwards a rufescent tint.
Notes on Stereocaulon buchanani, Stirton.
The valuable report of Dr. Stirton on Buchanan's plant has been brought
under my notice white it was passing through the press. The following notes—with the analysis made some years since—will be found useful. The plant has been named by Dr. Nylander (in a letter)Lecidea subglobosa
Dr. Stirton's follow pretty closely parts of Nylander's desription of the genus Gomphillus, Nyl. There is, however, an essential difference in the structure of the thallus from that of the Gomphillus, which is overlooked by Dr. Stirton, but which is strongly in support of his view that the plant should be classified under the genus Stereocaulon. In Buchanan's lichen the thallus is made up of gonimia, as in Stereocaulon, instead of gonidia as in Gomphillus. Nylander's description of the genus Gomphillus would apply if “gonimia” was substituted for “gonidia,” thus: “Thallus tenuissimus,e gonimiis [gonidiis] mediocribus sphericis elementisque filamentoso-irregularibus gelatinose conglu-tenatis constans.” The paraphyses are indistinct only from their exquisite fineness and compactness; not, I think, from the “tenacious stiff gelatine which pervades the hymenium.”
The filaments which bind the gonimia together are few and scattered. The spores are 0.160 millim. long, and 0.003 millim. broad.
Plate XXV.—Stereocaulon buchanani. Fig.1,Section of apothecium with portion of thallus. 2, Gonimia. 3, Gonimia, with filaments. 4, Spores.