58 MR. W. WEST : ECOLOGICAL NOTES. 
approach anything like exhaustion. А large number of trees have been 
examined in various parts of the British Isles, away from the pernicious 
influence of smoke. The results will be seen to be varied, the variation 
being due to different kinds of exposure, the different age of the trees, their 
aggregation or complete or partial isolation, the amount of rainfall, the 
proximity of mountains or sea, as well as other factors. — Stereodon cupressi- 
formis var. filiformis is generally the most prevalent corticolous moss, yet in 
some districts with a heavy rainfall, as parts of Kerry, Argyll, Cumberland, 
&с., Isothecium myosuroides becomes the most abundant epiphyte, and it is 
often quite dominant on the lower part of the trunks, when it hardly or does 
not at all extend above. When the trees are subject to a drive of wind from 
the mountains with much rain, as at Capel Curig, Lecanora tartarea is some- 
times a dominant epiphyte, with Platysma glaucum often as a subdominant. 
As a general rule Parmelia saxatilis is the most abundant epiphytic lichen. 
The following rough percentage records will illustrate the point further, 
and especially as showing much variability, so much so at times, without 
very apparent cause, that one wonders whether the prevalence of one or 
another kind is not sometimes due to the earlier time of the arrival of the 
successful epiphyte on the unoccupied places. 
CorTIcoLous ASSOCIATIONS (chiefly). 
OBSERVATIONS IN SCOTLAND. 
Inverary. Average rainfall, 83 inches ; average of total days of 
rain, 225. 
The approximate percentage of: sub-bareness * on 15 Beeches (see р. 59) 
was 16, the average percentage of epiphytes 84, made up thus :—Stereodon 
cupressiformis (35), Frullania dilatata. (2), Parmelia saxatilis (4), Per- 
tusaria spp. (61), Ricasolia amplissima (21), R. letevirens (4), Lobaria 
monaria (8), crustaceous lichens (81). 
Stereodon resupinatus, Graphis scripta, Evernia Prunastri, Ramalina 
farinacea, R. fastigiata, Stictina fuliginosa, and a few other lichens occurred 
on these beeches in small quantity. Polypodium vulgare was also a frequent 
epiphyte. Sometimes Mnium hornum crept up the trunks for a short 
distance from the ground. The lichens were mostly on the exposed sides, 
the bryophytes on the less exposed ones. 
* The term sub-bareness always includes variable quantities of small scattered patches of 
crustaceous lichens such as Lecanora subfusca, Lecidea parasema, Graphis spp., &с. 
