August 21, 1884] 



NATURE 



393 



Sitka Island ; Mackenzie River, 65 ; Canada ; Labrador, 

 58° 45' ; 1 Greenland. 



Zea mays, L. (Indian corn). This plant requires also 

 a very warm summer to ripen its seeds. In England it 

 can only be cultivated as a green vegetable ; on the 

 western shores of Europe we can say that the cultivation 

 is only profitable to the 46th degree N. lat., and in the 

 valley of the Rhine it reaches to 49°. In North Germany 

 the grain usually does not ripen. In North America, 

 however, it is cultivated in certain regions with profitable 

 returns up to 5 1 3 N. lat. 2 The period of vegetation varies 

 there between seven and three months. To cultivate the 

 varieties of such a short period in Europe is tried, but 

 without result ; they were transformed after a few gene- 

 rations into the common corn. 



Thus we see that, of the plants just named, the larch, 

 the pine, the birch, and the aspen grow in Siberia, with its 

 excessive continental climate, farthest to the north ; yet 

 many of the cultivated plants mentioned above, and 

 almost all those of the temperate zone, are either culti- 

 vated or grow wild in the sea climate of Norway, to very 

 high latitudes. 



On the north-western shores of America the pine at- 

 tains a considerable size (island of Sitka), in a climate 

 with continual rain, but partly the same size is observed 

 on the Rocky Mountains (eastern slope), where the climate 

 is wholly changed. 



In British Columbia the climate is continental, very 

 cold in winter ; yet the same gigantic trees as on the 

 coast are to be found here ; precipitation takes place in 

 spring, but the amount is very great. 



In California, with its largest coniferous trees of the world 

 ( Wellingtonia gigantea), rain falls chiefly in winter (No- 

 vember to April). The enormous differences of coast and 

 inland climates of California are not apparently known. 



In the southern parts of the Amur region in Asia there 

 is in summer a luxuriant vegetation ; the annual precipi- 

 tation amounts to 27 '56 inches (about the same amount 

 as in Germany), the plants much resembling those of 

 Central Europe, 3 and this notwithstanding a winter tem- 

 perature much lower than observed in the most northern 

 parts of Lapland ; but the summer here is much warmer 

 than in Europe under the same latitude, and precipitation 

 occurs o?ily in summer. 



In the interior of Siberia the vegetation consists chiefly 

 of coniferous trees ; thus the luxurious growth in the re- 

 gion just named must be caused by the influence of the 

 sea climate, as Middendorff suggests, 4 though there is a 

 mountain chain on the east coast. The extensive forests 

 of Russia and Siberia prove that an extreme continental 

 climate is resisted by some coniferous and other trees, 

 but it is evident that in general a sea climate with mild 

 winters, and thus a long period of vegetation, suits them 

 best. 



As we have seen, the northern limit of the cultivation 

 of corn reaches on the continent a much higher latitude 

 than on the shores. On the north-west coast of North 

 America the island of Sitka (57 N. lat.) and Kadjak 

 are on the extreme limit. On the Faroe Isles, barley 

 (this can only be the coarse variety) is cultivated, but the 

 grain very seldom ripens ; 5 the cause is absence of sunlight 

 on account of the continual cloudy sky, storms and pre- 

 cipitation, causing low temperature in summer (mean 

 temperature at Thorshaven, July, 49°'8), for corn wants a 

 sunny climate, and to be under the direct influence of the 

 sun's rays. This explains why it can be cultivated within 

 the Polar Circle (Norway), where the sun in the summer 

 season remains constantly above the horizon. 



In North America, on the shores of Hudson's Bay, the 

 tree limit goes down to 59°, the corn limit to 50 (Ontario). 



1 Petermann, Geogr. Mittheilwtgen, 1859, P- I2 4- 



2 Richardson, vol. ii. p. 267. 



3 Kittlitz, " Vierundzwansig Vegetationsansichten von Kiistenlandern und 

 Irseln des Stillen Oceans," p. 53. 4 Middendorff, p. 763. 



5 Martins, " Sur la Vegetation de l'Archipel des FeroiV 



On the shores of the Okotsk Sea corn cannot be culti- 

 vated at all, even on the south coast, under 50 N. lat. In 

 Greenland the culture of corn is also impossible. The 

 causes are the same as said above : the sea winds, wet 

 climate, and fog in summer — thus want of sunlight. 



Of all the cultivated vegetables, Raplianus sativt/s, L., 

 et var. (radish), Brassica rapa, L., et var. (turnip), and 

 Brassica Napus, L., et var. (rape), grow as far north as 

 there are settlements — in Norway beyond 70 N. lat. ; in 

 Siberia to the Polar Circle ; on the north-west coast of 

 America to 64 45' (Nulato), and Redoute St. Michael, 

 63° 30', in the interior to 67° (Fort Good Hope). 1 In 

 Greenland rapes, turnips, cabbage, and salad are culti- 

 vated under 70 N. lat. (Island Disko). 



The potato follows the above-named plants in their 

 distribution to the north, and belongs also to the sea 

 climate ; at its northern limit in Siberia, however, as well 

 as in North America, it is the size of a walnut. 2 In 

 Greenland only the most careful treatment can produce 

 eatable ones. The plant never blossoms here. 3 



When comparing the vegetation of the extreme con- 

 tinental climate with that of the extreme sea climate on 

 the globe, the continental has the advantage ; the South 

 Shetland Isles, in 6o°-63° S. lat., are at the most 

 southern limit of phanerogamous plants (only a grass, 

 Aira antarctica, Forst., is found here), and on Cockburn 

 Island (64 S. lat.) the last trace of vegetation is found 

 (cryptogamous plants). At this latitude north there is in 

 Siberia a forest of very high coniferous trees. In the 

 Antarctic regions there are several causes why vegetation 

 ceases at such a low latitude, but these are all conse- 

 quences of the chief cause, viz. the fact that the whole 

 southern hemisphere, with the exception of relatively small 

 spaces, is covered with water; severe storms 4 combined 

 with a very low summer temperature 5 banish all vege- 

 tation. 



The extreme continental climate has also its disadvan- 

 tages, but chiefly with relation to the cultivation of corn. 

 In the first place corn is very often destroyed by night 

 frosts ; they make the harvest uncertain. 



The constantly frozen ground is the chief cause why 

 corn cannot be cultivated in Siberia beyond 62° (Yakutsk). 

 The temperature of the soil in which the roots vegetate 

 varies between 36 and 41". Thus notwithstanding the 

 mean temperature of June at Yakutsk being 57^ and that 

 of July 62 , 6 the vegetation is relatively slow, though its 

 period is the same as observed in Central Europe (ten to 

 twelve weeks). 7 The same period is observed in North 

 America, at 63 (Fort Simpson), of the barley (wheat 

 does not come to maturity here). But harvests of thirty 

 to forty times the amount of what was sown alternate 

 in this climate with years of no harvest at all. 8 It is 

 known that the native plants withstand the lowest tempe- 

 ratures of the Siberian winter. 



Returning to Europe, we have seen that even the 

 climate of the northern parts of the British Isles is not 

 suited for many vegetables and other cultivated plants. 

 It is Germany which has a climate where we can find 

 almost all the plants of the temperate zone and those 

 commonly cultivated ; we see the vine in this country 

 ascend farthest to the north, while corn and all vegetables 

 ripen their seeds perfectly. It is clear that the climate is 

 best suited for the vegetation of this latitude. 



Now if we compare the mean temperature of July in 

 Germany with the mean for the latitude (for 50° N. lat. 

 62°) calculated by Dove, we find that even in this country 



1 Richardson, vol. i. p. 214. 2 Middendorff, p. 700. 



3 Von Etzel, "Gronland geographisch und statistisch beschrieben," p. 282 

 (Stuttgart, i860). 



4 Lowest reading of the barometer by the United States Exploring Expe- 

 dition under Wilkes in lat. 65° 15', 27'5o (see " Narrative of the Expedition," 

 vol. ii. p. 281 (London, 1852). 



5 In lat. 64 5' mean temperature of January 1843, 31 6 ; in 62°-66° in 

 February, 31 (see Ross, "Voyage in the Southern and Antarctic Regions," 

 vol. ii. pp. 352, 360. 



6 Middendorff, p. 772. 7 //'. p. 718. 8 lb. p. 720. 



