DB. LINDBEHa'S CONTUIBUTIONS TO BEITISH BEYOLOOT. 461 



is desirable to get a clear view of the structure of the leaves of 

 mosses and Jungermannia?, especially about the nerve, the object 

 should be placed in a drop of a strong solution of caustic soda, 

 and, after a minute, washed in distilled water. By this means we 

 obtain a perfectly transparent object, with a sharp contour, so 

 necessary when we examine the Andrecece nervate^, Pleuridiay Di- 

 tricha {Leptotricha) ^ Seligerice, &c., whose leaves are often badly 

 described in books. 



II. Pottia intermedia, 



w 



This moss has been regarded by all recent authors as a 

 variety of P. truncatula^ but has some important characters, 

 from which it must be considered a distinct species (P. inter- 

 media (Turner), ruernr.), intermediate between P. truncatula 

 (L.), Lindb., and P. lanceolata (Hed.), C Mill. 



These characters are the size, the margin of the leaf more or 

 less revolute up to the middle, the long, often cylindrical cap- 

 sule, which is, when dry, indistinctly constricted below the nar- 

 rower orifice, the rudimentary peristome, and the compound 

 annulus closely adhering to the margin of the capsule. 



P. truncatula is, compared with this, a smaller plant, with the 

 leaves quite plane, and a short nearly globular capsule with 

 wide mouth, which, in the dry state, is much constricted below the 

 orifice, wanting also a peristome and annulus. P. lanceolata has 

 a narrower mouth to the fruit, and a well-developed peristome. 

 By the above characters P. intermedia bears to the other two spe- 

 cies {DesmatodonteSj Lindb.), the same relation that riiyscomitrium 

 eurystomum (a species probably occurring also in Britain) does 

 to Ph. spTicdricum and Ph. pyriforme, — difi'ering from the former 

 in its more robust habit, in the broadly lanceolate acuminate 

 leaves, which are serrate, not concave, but canaliculate, with cells 

 twice as long as broad, and by the obtusely conic lid ; from the 

 latter by its hemispherical capsule with very wide mouth, simple 

 annulus, short lid, &c. As the synonyms of Ph. sphcericum and 

 eurystomum are still very much confused, I add references which 

 may aid in their extrication, 



+ 



1. Phvscomitrium sph^ricum (Lud.), Brid. 



Gymnostomum sphsericum, Ludw. MS. ; Schkukr, DeutschL Moos, 

 p. 26. no. 15 (1810) ; Schwgn. in Schrad. Jour. Bot. ser. 2, iv. 

 p. 15 (1810), et Supp. i. pt. 1. p. 21. no. 6 (1811); N. IL S. Bry. 



^iyS, PKOC. — BOTANV, VOL. XI- 2 I 



