234 ORTHOTRICHACE^. 



A very distinct moss in its brilliant green colour and compact habit, forming large 

 smooth soft cushions on the sides and in the clefts of damp rocks. The fruit is not 

 uncommon, and when found is usually present in great abundance, the last season's 

 capsules often being found side by side with those of the year, and almost or quite 

 overtopped by the younger branches. It somewhat resembles Grimmia torquata, but 

 is of a brighter green, the stems more compact and far more coherent, and the leaves 

 of course entirely without hair-point. Zygodon Mougeotii differs in the longer leaves, 

 narrower in proportion to their length, and Weisia rupestris and curviroslris in the 

 duller colour as well as in areolation. 



The var. pellucidum is very distinct in the areolation, and as it has not been found 

 in fruit, its position must be held slightly uncertain. 



The leaves are not strongly hygroscopic as is almost universally the case in this 

 Order. 



48. ZYGODON Hook, and Tayl. 



Stems slender, dichotomously branched, leaves from oblong- 

 lanceolate to linear, usually twisted when dry. Capsule emergent 

 or exserted on a longer seta, 8-striate, with a distinct neck ; 

 peristome double, single or none ; calyptra smooth, cucullate. 



I have followed Bruch and Schimper and other authors in 

 uniting Amphoridium with Zygodon. Although the sub- 

 immersed capsules of Z. lapponicus, of a thicker consistency and 

 with a wider mouth, give the plant a very different habit to that 

 of the species with longer setae, it is only a question of a very slight 

 shortening or lengthening of the seta ; Z. Mougeotii, indeed, in this 

 respect approaches the species usually included under Zygodon, 

 and the differences resolve themselves into slight distinctions in 

 the form of the capsule, hardly sufficient to carry generic rank 

 when in so many particulars the plants are closely allied. 



Zygodon is nearly allied to Ulota and Orthotrichum, differ- 

 ing principally in the smooth, cucullate calyptra, the oblique beak 

 of the lid, and in the usually narrower leaves almost always with 

 plane margins. 



/Leaves toothed near apex 6. gracilis 



\ Leaves entire 2 



2 /Leaves wide, smooth, soft, hyaline at base ; cells over 15 fi .j. Forsteri 



\ Leaves narrower, more or less papillose ; cells under 10 p 3 



/Stems tall, matted ; Is. long and narrow ; seta very short 4 



•'XStems short ; Is. short; seta longer 5 



/Ls. much curled when dry ; basal cells thin-walled 1. lapponicus 



4 \Ls. scarcely curled ; basal cells incrassate 2. Mougeotii 



/Nerve excurrent in a mucro ,j.* Stirioni 



■'(.Nerve vanishing below apex 6 



g/Peristome absent ; ls. spreading, recurved .3. viridissimus 



\ Peristome present ; ls. patent, not recurved ^. conoideus 



