324 



when the atmosphere ceases tq 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 existence. How they find their way to such places, 

 and under what laAvs they are created, are mysteries that human ingenuity 

 has not yet succeeded in unveiling. About 800 species are known. 



Properties. The slight astringency of Polytrichum and others caused 

 them to be formerly employed in medicine, but they are now disused. In 

 the economy of man they perform but an insignificant part ; but in the 

 economy of nature, how vast an end ! 



Examples. There is no settled arrangement of the genera, almost every 

 writer having a method of his own. Much merit is due to several, especially 

 to that of Greville and Arnott, published in the Wei-nerian Transactions^ 

 vols. 4. and 5. 



Sphagnum, Hypnum, Bryum, Fontinalis, Gymnostomum, Dawsonia, 

 Weissia, Phascum. 



CCLXVIII. HEPATIC.^. The Liver-wort Tribe. 



Hepatic^, Juss. Gen. 7. (1789); Dec. Fl. Fr. 2. 415. (1815); Agardh Aph. 104. 

 (1822) ; Greville Flora Edin. xv. (1824) ; F£e in Diet. Class. 8. 131. (1825.) 



Diagnosis. Flowerless terrestrial plants, with their sporules contained 

 in dehiscent thecse, destitute of an operculum. 



Anomalies. Riccia has indehiscent fruit immersed in the substance of 

 the frond. 



Essential Character — Plants Rowing on the earth or trees in damp places, 

 composed entirely of ceUular tissue, emitting roots from their nnder-side, and consisting of 

 an axis or stem, wliich is either furnished wjth leaves, or leafless, and then bordered liy a 

 membranous expansion ; these expansions sometimes unite at their margins, so as to form 

 a broad lol)ed tlialhis. Reproductive organs of several kinds ; eitlier a 1- 2- or 4-valved 

 theca, supported upon a membranous peduncle, covered when young by a leaf, through 

 which it afterwards protrudes, and often containing spiral fibres, called Elateres, within 

 which the sporules are intermixed; or a ])ellate stalked receptacle, bearing thecie on its 

 under surface ; or sessile naked thecpe, either immersed or superficial. Besides these there 

 are in Jungermannia " miimte, spherical, membranous, retic\ilated bodies, supported upon 

 short white peduncles," {Grev.)\ in jMarchantia, "peltate receptacles, plane on the upper 

 surface, and having oblong bodies imbedded in the disk;" and also "little open cups, sessile 

 on the upper surface, and containing minute green bodies (gemnue) which have the power 

 of producing new plants, as well as the sporules;" and in Anthoceros, " small cup-shaped 

 receptacles, containing minute, spherical, pedunculated, reticulated bodies." 



Affinities. The structure of the reproductive organs of this order is 

 so exceedingly variable that no common character seems deducible from 

 them ; nor has it been found possible either to determine what analogy exists 

 between the organs, or even to decide what their respective functions are. 

 What are here called the thecse are considered to be the cases of the sporules, 

 properly so called, but the other bodies are of a more doubtful kind. Those 

 who have sought for sexual organs in Cryptogamous plants have naturally 

 taken the imbedded oblong bodies of Marchantia, and the pedunculated reti- 

 culated ones of Jungermannia, for anthers; but- J)r. Hooker, in his beautiful 

 Mouof/riiph of the latt(;r genus, and also in his Briiish Flora ([>. 459.), is 

 evidently unsatisfied as to their nature. Dr. Grc.'ville, in the Flora Edineiisis, 



