PEE eh as i ee te atieh  M ei ES eS 
Special Morphology and Classification, — 303. 
Seg simple structure. They usually consist, with the exception 
of the veins, of only a single layer of parenchymatous cells ; 
Fic. 427.—Hair-moss, Polytrichum commune; I. plant with theca (magnified) ; 
II. theca with calyptra, III. without calyptra (magnified); IV. plant with 
perigonium surrounding the antheridial receptacle, and exhibiting prolification 
(magnified) ; V antherozoid (x 1000). 
but exceptions occur in the case of Sphagnum and other 
Mosses. In folytrichum the surface also has cells pro- 
