187 . 



otlior thiiifjs boiiio; equal, vo<2:otatioii is much more active on high 

 phiteaus. where the radiation is or(>ater. as well as in loealili<'s where 

 the annual variations are very marked '. This activity is further reeii- 

 foreed if the locality is near the polar re«2:i()ns, where the light acts 

 almost uninterruptedly when once the awakening of the plants 

 has taken place. In this respect Russia and Lai)land present us with 

 notable examples of this reenforcement. 



Kui)rt'er, 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 reoion : 



"A comparison of the curves for Nertchinsk, Irkutsk, and Arch- 

 angel demonstrates in a striking manner,'' says Kupifer, " 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, Avhence 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 be(;omes 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 temj^erature between the warmest and the coldest month 

 of the vear 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 temi)erature 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 rei)resent that of the ])lants. 

 In this respect the conditions of vegetation would be the same at each 



