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THUIDIUM BEGOGNITUM (Hedw.) Lindb. and its Allies. 

 By H. N. Dixon, M.A. ; F.L.S. 



The difference between Thuidium tamariscinum (Hedw.) 

 B. & S., T. delicatulum (Hedw.) Mitt., and T. recognition (Hedw.) 

 Lindb., was first clearly pointed out by Lindberg (Manip. Muse. 

 ii. 415, in Notiser Sallsk. Fauna et Fl. fenn., forh. xi. 1870). 

 These differences may be briefly tabulated thus : — 

 Apical cell of branch-leaves acute, smooth ; peri- 



chaetial leaves ciliate tamariscinum. 



Apical cell of branch -leaves cylindrical, truncate, 

 crowned with 2-4 papillae — 



Perichgetial leaves ciliate delicatulum. 



Perichaatial leaves not ciliate recognition. 



In that paper Lindberg gave the first European record of 

 T. delicatulum (the common North American plant), viz. from 

 Hogland, an island off Finland. It was not recognized as a 

 British plant in the London Catalogue of British Mosses, 1881, 

 nor by Hobkirk (Synops. of Brit. Mosses) in 1884. It was first 

 detected with us by Mr. Holt, at Tyn-y-groes, N. Wales, in 1885. 

 In 1895 I gathered it fruiting at Lodore, where the Kev. C. H. 

 Binstead also had gathered it in 1889, taking it for T. recognitum. 

 These two localities are all that were known in 1896, when the 

 part of Braithwaite's British Moss Flora dealing w T ith Thuidium 

 was published. I have now ten sheets of T. delicatulum in my 

 British herbarium, from about twenty distinct localities, collected 

 by myself, besides half a dozen specimens sent by other collectors. 



In 1893 Philibert described a fourth species of this group as 

 T. intermedium ; this name, however, having been already em- 

 ployed by Mitten for a New World species, Limpricht rechristened 

 it T. Philiberti. The most conspicuous feature about this species 

 was the long acumen of the stem-leaves, ending in a filiform point 

 consisting of a single articulate thread of several linear cells. This 

 species I gathered in Perthshire in 1893, and recorded as T. Phili- 

 berti in Journ. Bot. 1897, p. 16. Dr. Best, who had then very 

 carefully studied these plants, confirmed my determination, adding, 

 " it always grows in wet places." 



As I understood the plants at that time, they could be fairly 

 well separated with the aid of ecological characters. Thus 

 T. tamariscinum was almost entirely a woodland plant, fairly 

 universal, and known at once by the smooth, acute apical cell of 

 its branch-leaves from the others. T. delicatulum was a plant of 

 moist, siliceous soil in mountain woods or by waterfalls, frequently 

 growing in sand by mountain streams, and entirely absent from 

 the eastern parts of our islands, at least south of the Firth of 

 Forth. It was to be known generally by the delicate, always (or 

 nearly always) tripinnate branching, the shortly pointed stem- 

 leaves, resembling those of T. tamariscinum, and the ciliate 

 perichaetial bracts. T. Philiberti was a rather large, straggling 

 plant, sometimes bipinnate, more usually tripinnate, always found 



