MOSSES WITH A HAND-LENS 51 



FAMILY 8* GRIMMIACEAE. The Grimmia Family. 



OR a long time most members of this family seemed 

 too difficult to study with a hand-lens, but nearly 

 all the more common forms can be distinguished if one 

 knows what to look for as characteristic of each 

 species. The plants grow in tufts or mats and almost 

 always grow on rocks. They are dark-brown or blackish, 

 often green at the surface of the tufts where the young grow- 

 ing portion of the plant is. In many plants the leaves end in a 

 whitish hairlike point that gives the plants a gray or hoary ap- 

 pearance. It is of great importance in determining the species 

 to find out whether the margins of the leaves are plane or 

 recurved when dry, and this can readily be made out by 

 a careful examination with a hand-lens in a strong light. In 

 appearance the plants of this family are much like those of the 

 Orthotrichum Family, but in the Grimmia Family the calyptra 

 is never hairy; the capsules are smooth when dry or at most 

 irregularly wrinkled; the peristome single with the 16 teeth 

 sometimes spreading but never reflexed, often forked, but never 

 united in pairs; leaves never crisped (except Ptychomitrium). 

 In the Orthotrichum Family the calyptra is often hairy, the 

 capsules are nearly always deeply plicate when dry with 8 or 16 

 regular folds; the peristome is double, though the segments are 

 often very narrow; the 16 teeth are often united in pairs, and 

 nearly always strongly reflexed when dry, sometimes bending 

 so far back as to touch the capsule wall ; and the leaves are often 

 crisped, although not so in the genus Orthotrichum. With few 

 exceptions the plants of the Orthotrichum Family grow on the 

 trunks of living trees. 



Two species (Orthotrichum anomalum and U lota Americana) 

 of the Orthotrichum Family grow on rocks, both have hairy 

 calyptras and a double peristome. Some species in both families 

 lack the peristome. Some species of Andreaea when sterile are 

 hard to distinguish from this family, but nearly all are subalpine. 

 Farther distinctions are found under Andreaea. 



KEY TO THE GENERA. 



Leaves crisped, without whitish tips, costate; capsules long ex- 



serted Ptychomitrium 



Leaves not crisped, with whitish tips and no costa; capsules im- 

 mersed Hedivigia. 



Leaves not crisped, costate, whitish tips present in some forms, 



absent in others; capsules immersed or exserted 



Grimmia and Rhacomitrium 



