NUTRITIVE ORGANS OF CELLULAR PLANTS. 311 



The leaves arise along the stem, sometimes joined 

 together at their base, sometimes collected into rosettes, 

 or terminal buds, at others, alternate or spiral, along the 

 stems, shoots, and branches : they are almost always 

 sessile and sheathing at the base. They have the form of 

 little scales, oval or elongated, rarely obtuse, but almost 

 always pointed or acuminate, sometimes prolonged into 

 a long ciha, or, as it were, rolled into a cirrhiform point. 

 Bryum macrocarpum presents this singular appearance, 

 the leaf being entire and prolonged into a branching 

 ciha. Their colour is of a beautiful green, but some- 

 times they are naturally scaly, or transparent at the 

 apex; some are devoid of all nerves, and formed entirely 

 of homogeneous, nearly round, cellular tissue ; others 

 present near the middle a nerve of variable length, 

 which sometimes reaches the apex, sometimes stops in 

 the middle, and sometimes is only visible at the base. 

 These differences are observed in species elsewhere very 

 similar, and demonstrate the slight anatomical import- 

 ance of these nerves ; they are, in fact, only formed of 

 elongated cellules, which, by uniting together, resemble 

 the nerves of vascular leaves. 



All the leaves "of Mosses are continuous with the 

 stem, and never fall off of themselves; they remain a 

 long time dried at the base of the stems of those in dry 

 situations, but in those of damp places they are de- 

 stroyed by maceration, and then, if they have no nerve, 

 or only a very weak one, the stem becomes naked ; if, 

 on the contrary, the nerve is strong, it remains under 

 the form of a hair, or small spine, after the maceration 

 of the surrounding parenchyma; this is observed in 

 Fonti7iaUs, and the aquatic species of Hijpnum, 8cc. 



The ordinary leaves of Mosses have the margin some- 

 times entire, at others serrated ; sometimes these teeth 

 are so fine and numerous that the leaf appears cihated ; 



