SPIIAGNACE^E. 357 



Tetraplds pellucida, where the leafy axis frequently bears 

 a terminal cup-shaped receptacle, containing many lenti- 

 lorm stalked gemmae ; these separate spontaneously, and 

 give rise to a kind of protonerna, and upon this buds after- 

 ward arise, from which leafy axes are developed. Many 

 Mosses reproduce themselves by the formation of a pro- 

 tonema from the leaves and the root-hairs, and from buds 

 formed upon such a protonema new plants may arise. Even 

 the protonema is capable of an asexual reproduction of itself ; 

 sometimes its individual cells become rounded, spontane- 

 ously separate themselves, become thicker walled, and then 

 remain inactive for a time ; they thus remind one of the 

 conidia of some Thallophytes. 



There are four well-marked orders'of Mosses, as follows : 



Order Sphagnacese. The plants of this order are large, soft, and 

 usually pale colored ; they inhabit bogs and swampy places, and are 

 known as the Peat Mosses. The protonema is a flat thallus, or com- 

 posed of. branched filaments, accordingly as it has developed upon a 

 solid substratum or in water ; the leafy axis is usually much elongated, 

 and as it dies away below it grows at the summit ; the leaves are usu- 

 ally five-ranked, and are composed of two kinds of tissue, viz., (1) one 

 made up of small chlorophyll-bearing cells, and (2) one made up of 

 large perforated cells ; the latter are usually filled with water, and to 

 them is due the well-known power possessed by the Peat Mosss, of 

 retaining moisture for a great length of time. Root-hairs (rhizoids) are 

 present only in young plants, their place being taken by the reflexed 

 branches, which are always abundant. 



The inflorescence is monoecious or dioecious ; the rounded (almost 

 spherical) antheridia occur singly by the sides of the leaves of catkin- 

 like branches (not axillary, as stated in some books) ; the archegonia 

 are developed upon the ends of certain branches (A, Fig. 244). The 

 ripe sporogonium (capsule or spore-case) is globose, or nearly so ; its seta 

 is short, but it is borne upon a more or less elongated pseudopodium, 

 which resembles a seta. The old archegonium (calyptra) is ruptured 

 irregularly by the growing sporogonium, and forms only a very imper- 

 fect Cap to the spore-case. In the development of the spores the cells of 

 a layer parallel to the surface of the upper half of the capsule become 

 modified as spore mother-cells (B, Fig. 244). At maturity a circular 

 portion of the apex of the capsule spontaneously separates as a lid 

 (operculum), and allows the spores to escape (C, Fig. 244, d). / 



The order contains but a single genus, Sphagnum, represented in 

 the United States by twenty-seven species. These are of some eco- 

 nomic account, as they furnish a most excellent material for "pack- 

 ing" in the transportation of living plants. 



