187 
other things being equal, vegetation is much more active on high 
plateaus, where the radiation is greater, as well as in localities where 
the annual variations are very marked? This activity is further reen- 
forced if the locality is near the polar regions, where the hight acts 
almost uninterruptedly when once the awakening of the plants 
has taken place. In this respect Russia and Lapland present us with 
notable examples of this reénforcement. 
Kupffer, in his “ Note relating to the temperature of the soil and 
of the air at the limits of the region of cultivation of cereals,” gives 
the following temperatures for the three principal boundary points 
of this region: 
Mean temperature. 
Longi- | Lati- | Alti- |— 
| : 
tude. | tude. | tude. oun | ee Spring. Sua: reece 
ut | anes 
e / oN Beet | OL, | (OF HO NN Or OOF 
AS GS Kee ee 101 15 | 52 17 | 1,300 | —0.25 | 14.1 0.2 | +12.5 + 0.8 
INGEGCC ING Ka eeees ne te coe Le ee Sie See OO) | 3.2 | 21.7% | 1.0 | +12.9 —2.9 
PATE ITT SO UME eee eS. fe ee || oe 2S ella Leases | +0.7 | —10.0 | —0.2 | +11.5 +1.5 
| | 
“A comparison of the curves for Nertchinsk, Irkutsk, and Arch- 
angel demonstrates in a striking manner,” says Kupffer, “ under 
what climatic conditions the cultivation of cereals can be carried on 
notwithstanding the lowness of the average annual temperature. All 
the curves agree together in spring and autumn, whence it results 
that it is especially the temperature of spring and autumn which 
influences the cultivation of cereals; it is in these seasons, in fact, 
that occur the two most important periods of the year for agricul- 
ture—the time of sowing and the time of reaping. In the cultiva- 
tion of rye autumn plays a still more important part, because rye is 
sowed also in autumn.” Kupffer calls attention in another part 
of his note to the fact that some kinds of farming are carried on 
where the soil below the surface is frozen. ‘“ Experiments in farm- 
ing,” he says, “ have been made at Irkutsk, on a very small scale it 
is true, but which in many respects have been a success. This is 
due to the fact that the soil becomes soft on the surface and is thus 
capable of developing the germs received by it; its mean temperature 
is above zero four months in the year, which is sufficient to ripen the 
cereals in a country where continuity of the sunshine makes up for 
the weakness of solar action. Snow often falls upon the sheaves, but 
still they harvest them.” These examples confirm what we have 
said in regard to annual changes of temperature. In no locality in 
the world are these variations greater than here; at Yakutsk the dif- 
ference of temperature between the warmest and the coldest month 
of the year is 50.9° C.; at Irkutsk, it is 24°.1; at Nertchinsk, 39.°1; 
at Archangel, 28.2° C. 
It might be said, it is true, that the average temperature of the year 
should not be considered here, not even that of the free air, so long 
as the plants are covered by snow to shield them, for in this case 
the temperature of the air does not at all represent that of the plants. 
In this respect the conditions of vegetation would be the same at each 
