TORTULA. 183 



Hab. Stones and walls, often on sandstone ; not common. Fr. spring, but not 

 confined to one season. 



Usually more slender than T. muralis, in wide patches, not in small cushions ; 

 and distinct from all but the var. astiva of that species in the short mucro ; I have 

 seen specimens of that variety, however, which could certainly not be recognised 

 except with the aid of the microscope, when the distinct, pale, yellowish border 

 marks off T. marginata from all the allied species. The pale red, slender seta gives 

 it a different appearance from ordinary forms of T. muralis and from T. Vahliana. 



12. Tortula muralis Hedw. (Bryum murale L. ; Barbula 



muralis Timm, Schp. Syn.) (Tab. XXVII. J.). 



In its typical form growing in small dense cushions, some- 

 times in extended patches, short, in its tallest state rarely \ an 

 inch high ; dull or bright green, hoary. Leaves patent, when dry 

 twisted and curled, oblong or elongate-Ungulate , obtuse ; margin 

 revolute, not thickened , slightly yellowish; nerve yellow, excurrent 

 in a long hyaline smooth hair, usually fully half the length of the 

 leaf; cells as in the last species, but without the marginal band. 

 Capsule shortly and rather widely cylindric, on a purple seta ; lid 

 rostellate ; peristome teeth from a narrow basal membrane, 

 spirally twisted. Autoicous. 



Var. /3. rupestris Wils. (Barb, muralis var. rupestris 

 Schultz). Robust, tall, more branched ; leaves larger, broader; 

 seta very long, sometimes one inch, capsule longer, cylindric. 



Var. 7. sestiva Brid. Short, densely gregarious in wider 

 patches, bright green ; leaves narrower, linear, nerve excurrent 

 in a green mucro or very short hair ; seta and capsule shorter. 



Hab. Walls and stones ; very common. The var. £ on wet rocks, etc., not 

 common. The var. 7 on shady sandstone and calcareous rocks, more rare. Fr. 

 spring. 



One of our commonest and in its typical form most distinct mosses. The var. 

 astiva is the only form that is at all likely to be mistaken for any other plant, e.g. , T. 

 marginata ; but the leaves are usually more twisted, the seta stouter and darker, and 

 in any case the leaf margin offers a crucial distinction ; although sometimes very 

 narrowly recurved, the double thickness renders it almost always darker and more 

 opaque than the rest of the leaf, whereas in T. margi?iata the border is paler and 

 more translucent, and its structure totally distinct. 



As in some of the other species of this section, two or three marginal rows of cells 

 are usually more pellucid and incrassate, and yellowish, thus forming a paler yellowish 

 band ; but owing to the recurving of the margin this character is only noticeable upon 

 careful examination. 



In very dry situations the tufts become very hoary with the elongated hair-points. 



13. Tortula canescens Mont. (Barbula canescens Bruch, 



Schp. Syn.) (Tab. XXVII. K.). 



Resembling the last species, but less pulvinate, densely 

 gregarious, bright green when moist, hoary only when dry. 



