MOSSES WITH A HAND-LENS 63 



Family 9. Tortulaceae, Tortak Family. 



HE family name is particularly appropriate, as not only 

 are the leaves twisted (often strongly crisped) when 

 dry in nearly all the species, but the peristome also is 

 strongly twisted in a large number of the genera. The 

 family is a large one with a very great range of 

 variation which is partly due to the degeneracy of several of its 

 members. The species here treated all grow on soil or crumbling 

 moist rocks and cliffs. Nearly all are short stemmed with 

 radicles present at base only. The leaves in nearly every case 

 have the basal 1-3 to 1-2 made up of thin-walled hyaline or 

 slightly colored cells, while the upper portion is made up of 

 minute thick-walled cells so that it appears nearly opaque. The 

 costa is nearly always strong and often excurrent. Astomum, 

 which is treated with Pleuridium, does not open its capsules by a 

 lid, and Pottia, which is treated with Physcomitrium, and Gymnos- 

 tomum have no peristome, but the great majority of the species 

 have a well developed peristome which may consist of 16 

 straight, slender, more or less divided teeth, or in many cases of 

 32 fine hairlike teeth spirally twisted in several turns (see Plate I, 

 Pigs. 6, 7, and 8.) The capsules are on rather long straight setje 

 and are usually erect and cylindrical or nearly so. 



KEY TO THE GENERA. 



1. Eeaves tapering gradually from the base to the acute apex 3. 



leaves increasing in width from the base upwards, or at least 

 not narrowed until near apex, broad in outline and rounded 

 at apex except for the costa, wliich often extends out into a 



long white hair 2. 



•^, Peristome of 32 filifoim strongly twisted teeth which arise from 

 a high basal membrane (basal membrane short in T, 



muralis) ' Tortula 



Teeth i6, short, not twisted Dcsmatodon. 



3. Peristome lacking. Plants common on wet ledges and cliifs 



where lime is present Gymnostomum. 



Peristome present, operculum falling as soon as detached 4. 



4. Leaves curled to slightly crisped, with margins revolute; basal 



part of leaf usually somewhat colored; peristome twisted. . . .Barhula. 

 Eeaves strongly crisped when dry with margins plane or rolled 



inwards and base usually hyaline 5. 



5. Peristome of 16 short teeth; plants small Weisia. 



Peristome of 32 slender twisted teeth; plants large for the 



family Tortella. 



GYMNOSTOMUM. 



If you can find a wet cliff with some lime in its composition 



