PTEROGONIUM. 367 



1. Pterogonium gracile Sw. (Hypnum gracile Dill. ; 

 Pterogonium ornithopodioides Lindb.) (Tab. XLIX. K.). 



In wide, close patches, dark green or brownish. Secondary 

 stems very slender, usually bare below, 1-2 inches high, above 

 with numerous clustered branches which are curved to one side, 

 slender, julaceous when dry with the leaves closely imbricated 

 and appressed, obtuse, or elongated and flagelliform, often 

 rebranched. Leaves widely cordate-ovate, rapidly and sharply 

 contracted to a longer or shorter acumen, the uppermost and 

 those of the smaller branches less suddenly and more shortly and 

 widely acuminate, or acute only; all concave, excavate at base, 

 not plicate, densely crowded, when moist spreading, when dry 

 closely appressed, rendering the branches julaceous ; sharply 

 denticulate towards apex, at back above sparsely scabrous with 

 minute ascending papillae ; margin usually plane ; nerve very faint 

 and short, sometimes quite wanting ; either double or single and 

 forked above, hardly reaching half-way. Median and apical cells 

 narrowly elliptical-vermicular , longer at base ; cells of basal 

 wings in many rows short, wider, rounded-quadrate, becoming 

 oval above, then elliptical-rhomboid, finally becoming uniform 

 with those of the median part ; in the shorter branch-leaves the 

 areolation is much shorter, wider, and more uniformly oval- 

 rhomboid, narrowly elliptical only at base. Capsule on a long 

 seta, erect or slightly curved, sub-cylindric ; lid conical, rather 

 obtuse ; peristome pale yellow, inner of short processes without 

 cilia, on a narrow basal membrane. Dioicous. 



Hab. Rocks and tree-trunks, mostly in sub-alpine districts. Frequent. Fruit 

 rare, autumn. 



The curved cylindrical branches all pointing the same way, and very terete and 

 julaceous, especially when dry, give this moss a somewhat peculiar and very 

 characteristic look. The branches vary considerably in slenderness, sometimes 

 becoming almost filiform when dry, but always exhibiting a marked difference of 

 aspect between the moist and the dry state, so as hardly to look like the same plant. 

 It has some resemblance to PterigynandrumJiH forme, but that is a more delicate plant 

 with the stems less dendroid, the branches more slender, the leaves much smaller and 

 less pointed, and the areolation papillose. Eurhynchium circinatum is also some- 

 what like it, but with shorter, more equal branches, and the nerve strong and well 

 defined. 



The scabrous denticulations on the back of the leaf, most noticeable in the upper 

 leaves of a branch, are not of the nature of papillae as in Pterigynandrum and other 

 genera of Leskeacea;, but are more akin to the spines on the backs of the leaves of 

 Catharinea, etc. , on a minute scale. Boulay unites this species with Isothecium (some 

 species of which have the leaves similarly scabrous), and with some reason ; the basal 

 areolation is however different ; and the close imbrication of the leaves is a distinctive 

 feature of this plant. 



