LICHENOLOGY OF ICELAND 7 We À 
Type Ill. 
(Wet mountain heaths; level or knolly; snow-covering of long persistence; 
on the whole rich in lichens). 
Ex. 1. Vaölaheidi; the vegetation upon the knolls 
(North Iceland). 
wart willow ......... F °/o 90 Cassiope hypnoides.... F °/o 40 
FYDELACEÆ 0e 0 F °/o 90 Salma 4.2242, «2 F °/o 20 
Polygonum viviparum .. F °/o 90 Mosses Es Bee F °/o 100 
PIPE: . -......:.. F °/o 40 Eichens 2 1 Ravan. F °/o 100 
Bilene acanlis.......... F °/o 70 
Ex. 2. Vegetation upon the knolls on a heath on 
Husavikrfjall (North Iceland). 
Empeirum ........,., F °/o 100 Salix’ SPP - Fre an es F °/o 40 
Cee .. :....... F °/o 100 Grasses ei... Rae F °/o 20 
Vaccinium uliginosum.. F °/o 80 Alchemilla alpina..... F °/o 20 
Azalea procumbens.... F °/o 80 Erebens.4- le eee F °/o 100 
Ex. 3. Not knolly, level heath on Vadlaheidi 
(North Iceland). 
wart willow...«...... F °/o 95 Alchemilla alpina ...... F °/o 25 
PNDÉRACÉE . 0d. 0. F °/o 85 Eichen Ru a as F °/o 45 
Cassiope hypnoides..... F °/o 45 
As may be seen from the above description, the conception 
“heath” is rather comprehensive, in that many kinds of vegetation 
of fairly different physiognomy can be comprised under this name. 
Heaths however — as defined by me here — have one feature in 
common: they are all dominated by chamæphytes (about F °/o 100), 
in that sometimes one, sometimes another chamæphyte predominates, 
and sometimes they occur fairly equally mixed. In the meantime 
all chamæphytes are not equally hospitable towards lichens, for 
some, e. g. Salix lanata, dwarf birches and a few others, sometimes 
when they are well-developed, cast a deep shade and cover the 
ground abundantly with fallen leaves, and so they prove detrimental 
to the lichen-vegetation. Consequently the latter, partly from this 
reason and partly from others, vary as regards frequency-degree 
and mass-occurrence without its being possible to understand this 
fact by simply regarding the frequency-number (F °/o) of the chame- 
phytes in the tables. Other peculiarities, viz. the special specific 
peculiarities (high or low growth, small-leaved or large-leaved, etc.), 
luxuriant or stunted growth and similar features, cannot at all be 
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