STUDIES ON THE VEGETATION OF ICELAND 157 
TABLE 31. Agreement in Variation of Biological Spectra aud Species 
Group Spectra (cf. Text). 
or 
Ch | H |PhKTh | A |A3/A2, Al, E4| E 34241 
9/0 2/0 9/9 0/0 || 270 0/0 9/0 
Een nd Nes NESS BESES SEES a |35 | 50 15 » 
2 uen ee b |15 | 52 33 
Brick ie aeehvo ducs c | 3|50 47 
Iceland, 8—1200 m. above sea..... a \34 |53 is 80 | 58 38 5 
— 2 600 M EE ose co b |21|53 26 52 || 20 49 31 
— pi LUE SRE RE c 15152 33 40 115) 41 
Vestfirdir, 4—500 m above sea.... a | 43 50 7 93 | 50 | 50 » 
— A DOONAN. se oc 0e b | 31 |51 18 68 | 27 56 17 
— 01005: een c |17|52 31 411115 | 47 38 
Snow-bare vegetation Vestfirdir.... a 37 52 11 71 | 32 54 Pee: 
Normally snow-covered vegetation . b ‚24 55 21 50 | 13 55 32 
Constantly snow-covered vegetation c | 20 51 29 |28| 7 45 48 
Snow-covering class 1............. a | 47 41 12 172148 47 5 
— ØEN) RE b|34150| 16 60/35 51 14 
— STE eee eee c |27 158 | 15 134120 36 44 
direction; in all the spectra these two groups constitute about half 
the material. 
The effect of a changeintemperature is thus the same 
in both systems of indicators; but it is most marked in 
the species group system. 
Hence, when we have elsewhere in this treatise employed the 
species group and life form spectra when considering the external 
factors prevalent in the formations, this is quite justifiable; a spec- 
trum, particularly a species group spectrum, will thus be an im- 
portant guide in the determination of the external factors which 
are of importance for the vegetation. 
Variations in the density and number of species in the scale 
of external factors bring to light interesting relations. In the 4 classes 
of snow-covering Ia, Ib, II, and III, the mean density of species is 
respectively 2.3, 6.8, 13.3, and 10.2, and the mean number of species 
is 9, 24, 32, and 29; in the 7 classes of moisture the mean density of 
