STUDIES ON THE VEGETATION OF ICELAND 173 
of the three types of soil. Very striking is the daily variation in 
temperature, this is not only rather small at the surface, but already 
at very slight depths it is practically nil. 
Table 36 shows the average daily variation in temperature for 
sandy soil, clayey soil, and boggy soil, with or without a covering 
of vegetation i. e. of cornfield or wood. These investigations show 
the same conditions as table 35, viz. that sandy soil has a greater 
daily variation of temperature than boggy soil at the same depth, 
and that the daily variation in temperature penetrates to greater 
depths in sandy than in boggy soil. If the soil is covered with 
vegetation, i.e. wood or cornfields, the result will be in the first 
place a decrease in the daily variation of temperature. 
TABLE 37. Annual Variation of Temperature 
in Soils with different Vegetable Covering in Heinäis, Finland. 
After Th. Homén 1896, p. 147. 
Sh int <5 LES ee 5 
a1$| 31-4) >| 2] >| 34-e|ala| aie] é 
nel a | eel ee | se | ee Er trs 
CR ci a i a le RN P= 
> | fe = a ae A 
= ee = === 
Firwood 0.50 m | 1.6° 12 1.0 1.1 4.1 10.4 12.6 12.8 10.7 6.5 3.7 2.1 5.7 11.8 
1.00 > | 23 |18| 1.41.3|2.9| 7.5 10.0 | 11.010.0 |7.3|4.7|3.115.3| 9.7 
2.00 > | 3.6 |29| 2.41 2.2|2.6|471 7.0| 85| 871|7.7|5.8|4.3|5.0| 6.5 
Birchwood0 50 m | 1.0° 0.4 —0.2 0.3 23 7.5 102 10.9 94 5.6 3.0 1.6 4.3 11.1 
1.00 > | 2.0 15| 1.0/0.8|1.8| 4.9| 3.4| 8.7| 8.4 |6.3|4.3 | 2.9/4.2) 7.9 
2.00 » | 3.5 2.9 2622123) 3.9| 57| 7.0 7.5|6.8|5.6/4.4|45| 5.3 
Grassfield 0.50 m | 1.1° 06 0.3 0.4 1.0 46 85 9.8) 8.7 5.6/3.3 1.63.83 9.5 
1.00 > | 2.0 11.4! 10/09/11} 3.3] 65! 81| 7.9)6.1)42|2.7)3.8) 7.2 
2.00 > | 3.1 |2.4| 2:011.7|1.6| 2.3| 4.3) 5.8| 6.4) 5.9) 4.9 | 3.83.7) 48 
A similar series of investigations on annual variations in tempe- 
rature and temperature conditions is only found respectively for 
sunny open and wooded sandy soil, but unfortunately not for damp 
soil, whether such as is constantly damp throughout the year, or 
such as is damp in winter but dry in summer Table 37 (after 
Homén 1896) shows the annual mean temperature at various depths 
for respectively sunny open and wooded soil, the mean temperature 
of each month and the difference between the lowest and highest 
