STUDIES ON THE VEGETATION OF ICELAND 143 
the Arctostaphylos mo. Lyngdalur a, b, c, d, and e are respectively 
mosathembur, melar, transitional forms between mosathembur and 
mo, mo and geiri. Thrasaborgir a, b, and c are respectively mosa- 
thembur, mo and geiri. Lækjamåt a and b are melar and the high 
mo. Nordtunga a, b, and c are the mo, the vegetation in the forest 
glades, and the vegetation on the forest-ground. Arnarvatnsheidi 
a, b, c, d, and e are respectively melar, Betula-nana mo, the knolly 
mo, the vegetation on the sides of the snow patches, and the 
vegetation on the bottom of the snow patches with a northern 
exposure. 
A comparison of the mean values has been attempted and is 
likewise given in the table. The scale is divided into three divisions. 
I represents the types of vegetation bare of snow, melar (I b), and 
mosathembur (la). II represente types with normal snow-covering, 
viz. the mo. III represents types of vegetation with a constant 
snow-covering, i.e. geiri and forest. In the calculation of the mean 
values the deviating localities have been omitted, viz. Bjork a and 
‘b, Lyngdalur c, and Norötunga c. The figures under I a are thus 
the mean values of Lyngdalur a and Thrasaborgir a; Ib the mean 
values of Lyngdalur b, Lækjamét a, and Arnarvatnsheidi a. II re- 
presents Lyngdalur d, Thrasaborgir b, Lækjamôt b, Norötunga a, and 
Arnarvatnsheidi b and c. III, finally, represents the mean values 
of Lyngdalur e, Thrasaborgir c, Norötunga b, and Arnarvatnsheidi 
d and e. 
The distribution of species in the scale of snow-covering is as 
the distribution of species in the scale of moisture. Some species 
attain their maximum F.-percentage in class I, others in class II, 
others again in class III. Some species have a high frequency per- 
centage in one of the classes, others in two classes, either I and II 
or II and III; only a small number of species occur with a high 
frequency percentage in all classes. 
A comparison between the different scales of snow-covering 
shows in what uniform proportions the species occur in the different 
localities. It may be laid down as a main rule that the species 
react uniformly to the same changes in respect of snow-covering. 
A species which, in one locality, attains its maximum F.- percentage 
where there is a normal snow-covering but decreases if the snow- 
covering changes no matter in what way, will behave in the same 
way in all the other localities. 
