484 A TEXTBOOK OF BOTANY [Ch. XI 



in one large chamber but in many smaller ones separated 

 by sterile cells; and the surface tissue is chlorenchyma 

 which contains intercellular spaces and is covered with 

 an epidermis containing stomata and guard cells like 

 those of the higher plants, — this being the first appear- 

 ance of such stomata. Thus this sporogonium, like 

 the thallus, can synthesize its own food, though it is de- 

 pendent on the thallus for the supply of water and mineral 

 salts. Evidently the development of a root would make it 

 a complete plant, and in this case the two generations, the 

 gametophyte (thallus) and sporophyte (sporogonium) would 

 be entirely independent of one another vegetatively. This 

 is precisely what happens in some Pteridophytes, as will 

 later appear. 



Class 2. Musci: the Mosses 



These are well known to everybody, even sufficiently to 

 make "mossy" a word of familiar significance. They are 

 distinguished by the dense growth of their usually vertical, 

 slender stems, which bear spirally-arranged, very thin, small 

 green leaves, with long-stalked spore capsules rising above 

 the stems. These leaves and stems do not correspond mor- 

 phologically to the thallus or the leafy stem of Liver- 

 worts, but are rather special upgrowths from the actual 

 thallus, which consists of a system of creeping, branch- 

 ing, felted, green filaments called the pkotonema. They 

 occur in diverse situations, from hydrophytic to xerophytic, 

 but generally in drier places than the Liverworts. They re- 

 produce vegetatively in various ways, and sexually like the 

 Liverworts, but with more elaborate sporogonia. The 

 archegonia and antheridia are borne at the upper ends of 

 the stems, sometimes on the same but commonly on differ- 

 ent plants; and often they are surrounded by compactly 

 arranged and even somewhat colored leaves having an as- 

 pect which has suggested the erroneous name " moss flowers." 

 The sporogonium, on a slender seta, or stalk, is a somewhat 



