
NOTE ON THE SCHWENDENERIAN THEORY OF LICHENS. 245 

A very rare species on shady banks and mountains in Cornwall 
and North Wales is Philonotis rigida, the Rigid Apple-Moss. 
In the Pleurocarpus, lateral-fruited, division of Mosses two very 
common species, although not so common in fruit, may be mentioned. 
Hypnum rutabulum, the common rough-stalked Feather-Moss : 
this may be regarded as the commonest of the British Mosses ; 
growing everywhere on banks, walls and trees, and equally common 
throughout Europe and North America. It fruits both in the 
spring and the autumn, and takes its name from its very rough 
fruit-stalk (seta), the capsules of which are ovate-oblong, arcuate, 
and nodding (cernuous); leaves ovate, concave, acuminate, and 
serrulate, thinly nerved above half-way. Fig. 17. 
Hypnum populeum ; the Matted Feather-Moss, an equally com- 
mon species on stones, in shady situations, and greeting the eye by 
every wayside. The stems are creeping and sub-pinnate ; leaves 
narrowly ovate-lanceolate, tapering to a long serrulate point, margin 
reflexed, nerved to apex. 
Not so common as these two, but generally distributed through- 
out Britain, and found on stones by rivulets in shady woods, and 
sometimes in the water, is Wypnum rivulare, the river rough-stalked 
Feather-Moss, with deltoid-ovate leaves, gradually tapering and 
serrate, and only nerved above half way. Also fruiting in this 
month are Hypnum chrysophyllum, the golden-leaved Feather- 
Moss, fallow ground, chalk hills, etc., and Aylocomium Oakesit, 
Oake’s Feather-Moss, only found on alpine rocks in the Eastern 
and Western Highlands. 
Very rare and local are Zeskea apiculata (Myurella) found on 
moist rocky ground on Ben Lawers, and Leskea micans (Hypnum), 
on shady rocks in the South of Ireland. A little less rare are 
Leskia moniliformis (Myurella lulacea), Leskea.polyantha and Leskea 
subrufa, the last not fruiting in Britain. 
WILLIAM STANLEY. 
NOTE ON THE SCHWENDENERIAN THEORY 
OF LICHENS. 
By R. B, Crort, R.N., F.LS, F.RMS. 
| CANNOT better describe the theory as to the nature of lichens 
which is variously styled “The Algo-Lichen Hypothesis,” the 
“ Dual-Lichen Hypothesis,” and the Schwendenerian Theory of 
Lichens, than by quoting the commencement of a paper by the 
Rey. W. A. Leighton in ‘Grevillea’ (vol. ii, p. 122), in which 
periodical will also be found the arguments for and against the said 
theory. 

