Page:Journal of botany, British and foreign, Volume 9 (1871).djvu/12

 2 OBSERVATIONS ON THE SPECIES OF POTTIA.

viscid pruinosity, changing to crimson when touched. Annnlm evanes- cent. Gills free, very thin, moderately distant, somewhat veiitricose, white, the edge becoming crimson when touched. xS/;o?'e's white, "0003" x '0002". This species is scentless and tasteless, and the whole plant is extremely fragile. I have dedicated it to Miss Georgina Elizabeth Johnstone, Argyll Lodge, Campdcn Hill, in recognition of the Zealand success with which she has painted and studied the hyraenomycetous Fungi of Inverary.

Explanation of Plate CXTI. — Figs. 1, 2, 3, 4, 5. Agaricus CLepiota) Georgince, sp. nov. Fig. 6. Section of ditto. Fig. 7. Tratna. Fig. 8. Spores X 700 diameters.

��OBSERVATIONS ON THE SPECIES OF POTTIA ALLIED TO P. TRUNCATA, WITH DESCEIPTIONS OF THREE NEW SPECIES.

By William Mitten, A.L.S,

A specimen of the Pottia, mentioned by Dr. Braithwaite in the Au- gust number of this Journal, having been sent to me by Mr. Davies with a request that I would examine it, I have found it necessary in so doing to reinspect ray specimens and to look over the descriptions of the species.

" Pottia " has been generally accepted as the generic name for a group of species, chiefly European, all which have an intimate agreement among themselves in their mode and places of growth as well as their small size, foliage, and general appearance ; originally it was intended to include Gymnostomous species only, and those forms in Avhich a peristome is de- veloped were considered distinct and placed in the genus Anacalypta or TFeissia. In Mueller's Synopsis, Anacalypta is reduced to a section of Pottia, and in Schimper's ' Synopsis of the European Musci,' although both genera are first employed, at the end of the work it is admitted that they must be united.

These Mosses, with some other analogous species in other natural groups, offer great difficulties to the learner : it was formerly easy to examine the capsule for a peristome, — if it had none, the species might be Pottia, if, how- ever, a peristome was present, it must belong to some other genus ; if the peristome had short teeth, it might be Anacalypta, but when the teeth were elongated it became Desmatodon. Individuals of the same species differ greatly in the amount of the peristome ; in some examples the pe- ristome is a short membrane with or without the rudiments of teeth at its upper edge, and between this and the comparatively complete peristome proper to Anacalypta every gradation may be found. These gradations in the development of an organ upon which not a few genera have been established, lead to the question where is the most completely developed peristome to be found among Mosses evidently most closely related to Pottia ? The answer must be, in that group of the genus Torlula to which Syntrichia belongs, and the distinctions upon which Anacalypta, Besma- todon, and Trichostomum rest are barely of use as sections, for they fail to bring together the most nearly related species in every other particular except peristome. In several of the Pottias, even when the capsule is de- stitute of peristome, the cells of the opercidum are seen to be arranged in a twisted manner, so that — as stated in the " Musci Indici " (Journ. of the Linn. Soc. 1859), and since by Lindberg in his review of the European Trichostoma — the peristome, if developed, must be also twisted or the teeth ascend obliquely, as is commonly the case in Tortida.

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