TWENTY-I^EVENTH ANNUAL MEETING. 157 



long in Mnium and Fissidens), (see plates IV and XXI), or very minute 

 (1 mm.) as in the pseudopodium or Tetraphis, and Aiilocomnium. 



In some species there are two sizes of leaves, a row of larger leaves on one 

 side of the stem, and a row of smaller leaves on the other, as in Hypoptery- 

 gium, Rachopilum, and Cyathoparum. Other species have their leaves 

 larger and closer at the apex, termed rosulate, while they gradually grow 

 smaller, until they become scale-like at the base of the stem, as in Funaria, 

 Dicranella, Leptobryum, and others. The leaves may be very close, erect, 

 and overlap, termed imbricate, as in some species of Leucobryum, Thelia, 

 Leskea, and others (see plates V, XI, XXIV, and XXVIII); or the leaves may 

 be very distant, as in Webera albicans, Bryum argenteum, and others (see 

 plates XVIII and XIX). The leaves surrounding the floral organs usually 

 differ from those of the stem in size, shape, color and position, being often 

 crowded into a rosette, as in Mnium, Polytrichum, and otners. Some leaves 

 have stipular appendages at the base, called paraphyllia, which are thread- 

 like and chlorophyllose, and probably aid in assimilation. Paraphyllia occur 

 in many Hypna, and serve as distinguishing characteristics between its many 

 subgenera. (See plate XXXIII.) 



The leaves of mosses differ less in shape than in phanerogams, though there 

 is considerable variation. They are usually ovate-lanceolate, varying to or- 

 bicular, and subulate or awl-shaped. 



The base is often decurrent, auricled, or cordate, while the entire leaf 

 may be recurved, very concave, or even carinate. (See plates XXVI, XXIX, 

 XXyill, and XXXI.) 



The apex varies from broadly obtuse to long apiculate, hair- or awn- 

 pointed, and occasionally emarginate, while the two edges of the upper half 

 may be folded together, making it carinate: or the edges may be rolled in 

 towards the center, making it involute, or even tubular. 



The edges may be entire, serrulate, dentate, hispid, plane, revolute, in- 

 volute, crenulate, or wavy; while the border cells may be of different size, 

 shape; color, or thickness. (See plates.) The surface may be smooth on 

 both sides, papillose on one side only, or on both, and hispid or hairy. When 

 only one side is smooth, it is usually the upper. All these differences of 

 arrangement, form, size, margin, nad surface of the leaves are used in identi- 

 fication. All the species blend into each other, making the intermediate 

 forms very difficult to distinguish, even when closely studied with a micro- 

 scope. 



The leaves are sometimes ribbed or costate, and some are ecostate or 

 nerveless; while still others are bicostate, having two rudimentary nerves. 

 The costa may extend beyond the apex into an awn point, when it is^ called 

 excurrent. If the costa extends only to the tip of the leaf, then it is per- 

 current, or it may end in the middle of the leaf. 



The costa or nerve may be wide or narrow, thick or thin, round or flat, 

 smooth or hispid, or spinulose. It may also vary in color from green to 

 brown, or even purplish. In many species the costa is the distinguishing 

 feature. (See plates.) 



A peculiar form of leaf occurs in the genus Fissidens. in which the leaf 

 seems to be vertical, and to have two laminae for part of its length. The 

 split, or seemingly double part, is the true leaf; but the nerve or costa has 

 developed a lamina both on the upper and lower surfaces; which extend 

 beyond the true leaf more than its entire length, and faces horizontally. 

 (See plate IV.) 



In Polytrichum and Orthotrichum the nerves are made up of several 



