in their Influence on Vegetation. 357 
Solanum tuberosum L., Potato. Britain. Norway, 71° 7’. 
Russia, Pinega river, 65°. Turuchansk, 65°.  Yakutsk. 
Shores of the Ochostk Sea. Kamtschatka. Kadjak Island. 
Sitka Island. . Mackenzie river, 65°. Canada. Labrador, 58° 
45’.° Greenland. 
Zeat»Mays L., Indian Corn.—This plant requires also a very 
warm summer to ripen. In England it can be cultivated only 
as a green vegetable ; or the western shores of Europe the culti- 
vation is profitable only to the 46th degree N. L., while 
in the valley of the Rhine it reaches to 49°. In Northern Ger- 
many the grain usually does not ripen. In North America, 
however, it is cultivated with profitable returns up to 51° N. L.” 
The period of vegetation varies there between seven and three 
months. Cultivation of the varieties maturing in a shorter period 
has been tried in Europe but without success ; they were trans- 
formed after a few generations into the common corn. There 
must exist peculiar relations between the American climate and 
the vegetation of this plant. 
_thus we see that of the plants just named, the Larch, the 
Tine, the Birch and the Aspen go into Siberia, with its excessive 
continental climate, farthest to the north; yet many of the culti- 
vated plants mentioned above, and almost all those of the tem- 
perate zone, are either cultivated or grow wild in the sea 
climate of Norway to very high latitudes. 
he northwest shores of America the Pine attains con- 
siderable size (Sitka) in a climate with continual precipitation, 
but the same size is to some extent observed on the Rocky 
Mountains (eastern slope), where the climate is wholly different. 
In British Columbia the climate is continental and very cold 
In winter, yet the same gigantic trees are here to be found as on 
the coast; precipitation takes place in spring, but the amount 
IS very great. 
In California, with the largest coniferous trees of the world, 
( Wellingtonia gigantea), rain falls chiefly in winter (November 
to April); the other months are dry. The cause is known: the 
polar stream coming from the northwest reaches the Californian 
Coast under about 45° N..; the water being in summer muc 
colder than the land and the winds in this season mostly north- 
West, no precipitation can take place. This is the cause also of 
there being very little difference in temperature between summer 
e 
the gigantic vegetation of the west and northwest shores of 
North America. In Norway or Ireland, both having very wet 
1® Petermann, Geogr. Mittheilungen, 1859, p. 124. 
267 
1! Richardson, vol. ii, p. 267. A : 
San Francisco, winter 46°, summer 53°, year 51°. 
