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ORTHOTRICHUM. 



By a. J. Grout. 



Family Orthotrichace.^. 



Plants usually growing in short dense cushions on rocks or trees 

 blackish or brownish green, at least below. Leaves oblong-lanceolate or 

 linear-lanceolate, usually very hygroscopic; cells of the upper part, at least, 

 more or less rounded-hexagonal, often papillose. Capsule often immersed. 

 Calyptra often hairy. Peristome double or single, rarely absent, the teeth 

 often united in pairs. This family is usually united with the Grimmiaceae 

 on account of similar habit and facies, but the peristome characters are so 

 different as to fully warrant its separation. A general idea of these peri- 

 stomial differences is best obtained by an inspection of the illustrations. 

 Orthotrichum Hedw. 



Plants comparatively short stemmed, in close rounded cushions, some- 

 times looser, on trees everywhere, and more rarely on rocks. Leaves very 

 hygroscopic, imbricated when dry and not appreciably curled or twisted, 

 which character separates the genus from Weissia except W. Americana. 

 Upper leaf cells usually papillose, thick-walled, the lower thinner-walled 

 and quadrate to rectangular. Calyptra sparsely hairy or naked. Base of 

 seta enclosed in a minute cup-like sheath, the ochrea. Capsule immersed 

 or emergent, rarely exserted ; usually with 8 regular folds or plicae when 

 dry, but sometimes smooth or with i6 plicae. Peristome usually double 

 with i6 broadly lanceolate teeth, which are usually united in pairs. Inner 

 peristome of 8-t6 narrow segments, often called cilia. The paired (bigem- 

 minate) teeth and degenerate inner peristome illustrate well the de- 

 generacy of peristomes on erect capsules. 



A difficult genus, usually avoided by the amateur, but I believe one can 

 learn to recognize all the common species with a hand lens when they are well 

 fruited. It will usually serve to determine the number and position of the 

 teeth, markings of the capsules and general outlines of the leaves. Sterile 

 specimens are often indeterminable. The stomata furnish an excellent and 

 definite character and are easily observed by separating a capsule into two 

 or more divisions with the dissecting needles and mounting outside up ; the 

 stomata are nearer the middle of the capsule than in many mosses and are, 

 therefore, easier of observation. The condition of the material is of the 

 utmost importance. The capsule must be thoroughly soaked in hot water 

 for a long time to be fully expanded, and the dry capsule must be thoroughly 

 dry to be characteristic. The capsules of all species shrink progressively 

 with increasing age, and many varieties had their origin in this fact. The 

 plants should be moistened to determine whether the capsules are immersed, 

 emergent, or exserted. 



Key. 



I. Rock-inhabiting species ; peristome single, teeth i6, erector 



erect-spreading on dry capsules 2, 



Tree-inhabiting species ; peristome double, teeth usually 

 united into^S pairs, recurved or re flexed when dry .4. 



