37° LEUCODONTACE/E. 



with numerous paraphyllia, and less crowded leaves, which are more abruptly 

 acuminate, less revolute at margin, with looser basal areolation and generally longer 

 cells ; it is also quite wanting in the peculiar apical dentation of the present plant, 

 which frequently exhibits a double recurved tooth at the extreme apex, in the form of 

 a grapnel. This however is not always present, and the apex of the leaf is, moreover, 

 rather fragile and frequently lost. 



The capsules are, when present, produced in considerable numbers towards the 

 summit of the stems. 



This plant grows nowhere, perhaps, more 6nely in our islands than in Wistman's 

 Wood, Dartmoor, where it clothes the limbs of the old and stunted oaks with large 

 masses, hanging down to the length of a foot and more, and producing fruit in abund- 



92. POROTRIOHUM Brid. 

 (Thamnium B. & S., plur. auct.) 



Primary stem creeping, stoloniform ; secondary stems erect 

 (rarely depressed), dendroid, tall and robust, divided above, 

 •with numerous curved branches more or less turned to one side. 

 Leaves oval -oblong, of solid texture, strongly single-nerved, 

 toothed. Cells oval or rounded, small and short. Capsule 

 inclined and somewhat arcuate. Annulus present. Peristome 

 perfect, inner with a wide basal membrane, and with 3 

 appendiculate cilia between the processes. 



The usual name Thamnium (Bry. Eur.), of this genus, 

 had been previously appropriated 6y more than one author, being 

 applied to a genus of lichens in 1799 and subsequently to two 

 genera of flowering plants ; it must therefore be erased from our 

 bryological nomenclature. The name Porotrichum was first 

 applied by Bridel (as a sub-genus of Climacium) to the South 

 American species P. longirostrum (Hypnum longirostrum 

 CM.), with which the present species, according to Mitten, is 

 congeneric. 



On account of the perfect development of the peristome, the 

 genus has been by most writers placed among the Hypnacese, but 

 the nature of the areolation renders its position there anomalous, 

 and a perfect peristome is found in other genera which are by the 

 same authors separated from that Order ; it appears more logical 

 therefore to include it in the present Order, to which by the 

 nature of its leaves and areolation it properly belongs. 



{Ls. narrower at insertion than above, more or less ovate 1. alopecurum 

 Ls. widest at insertion ; branch ls. narrow, ligulate ; nerve wide ...2. angustifolium 



1. Porotrichum alopecurum Mitt. (Hypnum alopecurum 

 L. ; Thamnium alopecurum B. & S., plur. auct.) (Tab. L. B.). 



Secondary stems robust, erect or sub-pendulous ; dark brown, 

 rigid and unbranched at base, above divided into numerous 



