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alter their position from being inflexed with their points to the axis, to being re- 

 curved with their points turned outwards, — exactly what happens in flowering 

 plants ; the teeth of the inner peristomium often alternate with those of the 

 outer, thus conforming to the law of alternation prevalent in the floral leaves 

 of flowering plants ; and, finally, if we compare the various states of the 

 leaves of Buxbaumia aphylla with the teeth of Mosses, it is impossible not to 

 be struck with the great similarity in the anatomical structure of the two, 

 These are the considerations which have led me to the conclusion, that the 

 calyptra, the operculum, and the teeth of Mosses, are all modified leaves ; and 

 hence that the theca is to be considered more analogous to a flower than to a 

 seed-vessel. With regard to the membrane, or epiphragma, which occasion- 

 ally closes up the orifice of the theca, it may be considered as formed by the 

 absolute cohesion of the leaves of the peristomium, just as the operculum of 

 Eudesmia is formed by the cohesion of the petals ; and this is confirmed, first, 

 by Calymperes, in which the membrane ultimately separates into teeth, and 

 by the fact that the horizontal membrane exists more perfectly in such genera 

 as Polytrichum and Lyellia, in which there is no distinct peristomium. It now 

 remains to explain the internal structure of the theca consistently with the 

 theory that has been advanced of the peristomium, operculum, and calyptra. 

 I consider the theca to be merely the thickened apex of the arxis, the sporules 

 to be a partial dissolution of its cellular tissue, and the columella to be the un- 

 converted centre. That the end of the axis of plants frequently becomes 

 much more incrassated than the theca of Mosses, requires no illustration for 

 those who are acquainted with the spongy receptacle of Nelumbium, Rubus, 

 and Fragraria, the dilated disk of Ochna, the curious genus Eschscholtzia, or 

 Rosa, or Calycanthus, or, finally, the spadix of Arums. That the tissue is 

 frequently separated by nature for particular purposes, is proved by the produc- 

 tion of pollen out of the cellular tissue of an anther, and by the general law 

 of propagation that seems to prevail in flowerless plants, as Ferns, Lichens, 

 Algee, and Fungi ; the same phenomenon may be therefore expected in 

 Mosses. That the columella should be left in this dissolution of the tissue 

 might be expected, from its being a continuation of the seta or axis of de- 

 velopement, the tissue of which is more compact, and of course less Hable to 

 separation, than the looser tissue that surrounds it ; this is analogous to the 

 separation of the pollen from the connectivum of most plants, or from parts 

 only of the anther of all those genera which, like Viscum iEgiceras, or Raffle- 

 sia, have what, are called cellular anthers ; and to the very common separation 

 of the placenta, or a portion of it, from the dissepiments, as in Bignoniacea', 

 Ericeae, and many others. That it is presumptuous in me, who lay no claim 

 to reputation as a Cryptogamic botanist, to offer any opinion upon plants I 

 have only occasionally studied, I am fully sensible ; but I hope for the indul- 

 gence of the skilful Cryptogamist, in consideration of this having been the first 

 attempt to call his attention to the inquiry. 



Cteography. Mosses are found in all parts of the world where the atmo- 

 sphere is humid ; but they are far more common in temperate climates than in 

 the tropics. They are among the first vegetables that clothe the soil with 

 verdure in newly-formed countries, and they are the last that disappear when 

 the atmosphere ceases to be capable of nourishing vegetation. The first green 

 crust upon the cinders of Ascension was minute Mosses, they form more than 

 a quarter of the whole Flora of Melville Island, and the black and lifeless soil 

 of New South Shetland is covered with specks of Mosses struggling for ex- 

 istence. How they find their way to such places, and under what laws they 

 are created, are mysteries that human ingenuity has not yet succeeded in un- 

 veiling. About 800 species are known, 



