POTTIA. 167 



38. POTTIA Ehrh. 



Plants short, hardly branched, in tufts or scattered. Leaves 

 broad in outline, more or less ovate or oblong, usually papillose, 

 nerved almost always to apex or beyond ; areolation rather lax, 

 more or less hexagonal above. Calyptra narrow, cucullate. 

 Capsule erect on a straight seta, exserted, oval or cylindric, 

 cleistocarpous, gymnostomous, or with a peristome of 16 

 imperfect or lanceolate bifid teeth. Spores granulated. 



The species of this genus form a very natural group, and the 

 only real question of difficulty is whether they should stand alone 

 or form a section of Tortula. The convenience of the former 

 arrangement is obvious, since there are as many as 40 species 

 belonging to Pottia, and a still larger number to Tortula, and 

 although there is no doubt considerable affinity between the two 

 groups, it can hardly be considered closer than is often the case 

 between allied genera ; there is, moreover, a peculiar habit 

 among the Pottise which is only found in a few species of Tortula, 

 and which is there always associated v/ith the elongated fruit and 

 characteristic peristome of that genus. It is true that Tortula 

 pusilla and T. lamellata form a connecting link between the two 

 genera, and that the two being obviously inseparable, one must 

 be removed from what would certainly be its natural place did it 

 stand alone ; but the existence^ of such ambiguous forms is a rule 

 rather than an exception in nature, and to deny autonomy to all 

 groups that included such forms would be to reduce classification 

 to an absurdity. 



In Pottia the stems are usually very short, and never much 

 elongated; the leaves are usually soft, and generally spread in a 

 stellate manner from the stem when moist ; the capsule and seta 

 are almost always shorter than in Tortula, and the peristome 

 teeth are never filiform and elongated as in that genus. 



The quinquefarious or octofarious arrangement of the leaves 

 while no doubt a valuable character, and fairly easy of deter- 

 mination in fresh plants, is not of much use in the study of 

 herbarium specimens ; and even with the former it is sometimes 

 difficult, and occasionally, I am inclined to think, misleading. 

 Corbiere describes, for instance (Rev. Bry. 1895, p. 34) an 

 octofarious var. of P. lanceolata. 



Stomata are found on the neck of the capsule in most if 

 not all of the species ; I have observed them on P. recta, 

 bryoides, minutula, Starkeana, truncatula, intermedia , Heimii, 

 and asperula. 



