necessary to vegetable, during the period of vegetation. Thus, for instance, wheat requires about 12° (Réaumur) of heat during 140 days; that is, nearly 140 x 12° = 1680° Réaumur. In Venezuela, the sugar cane requires a longer time to grow in a higher and therefore cooler position than in a lower and warmer, and the length of time required is in proportion to the height. 196 Hence it is that the isothermal lines are not parallel with the equator or with one another. The greater number of these have two northern and two southern summits; the former on the western coasts of Europe and America, and the latter in eastern North America, and in the interior of Asia. 197 The quantity of rain which falls every year is, at St. Petersburg and Pesth, from 16 to 17 inches; at Berlin 19, Mannheim 21, Tübingen 26: in the interior of France 16-24; on the French coast 25, on the eastern coast of England 24, on the western coast 35, in Milan 36, Genoa 44, on the coast of most tropical lands 70-120. On the political-economical influences of most climates, see _Gobbi_, Ueber die Abhängikeit der Populationskräfte von den einfachen Grundfstoffen, 1842. 198 The snow limit at Mageröe in Norway is 2,200, in Iceland 2,900, in the northern Ural 4,500, in the Alps 8,200, in the Caucasus 10,400, and Quito 14,850 feet high. Hence it is that mountainous countries which produce nothing in the north, make magnificent vineyards in warmer countries. 199 In central Germany, even a second crop can be produced after the corn harvest. In Arabia, the same seed produces three harvests, because the grain which falls at the time of harvesting to the ground, germinates immediately and suffices for new seed. (_Niebuhr_, Beschreibung, 154.) 200 Thus in the northern states of the American union, wheat yields a return of only from four to five times the amount sown; in France, 5-6 times (_Lavoisier_): in Chili, 12 times; in northern Mexico, 17 times; in Peru, 18 and 20 times; in southern Mexico, 25 and even 35 times; in Germany, maize seed yields at best one hundred fold, while in the torrid zone there is a return of from three hundred to four hundred fold, generally. 201 Andalusian corn produces in the mill only one-half as much bran-waste as Baltic wheat produces. _Bourgoing_, Tableau de l’Espagne, II, 155. Baltic wheat contains 6-7 per cent, of azote, and Algerian, 20-25 Per cent. (_Kabsch_, Pflanzenleben der Erde, 1865.)