CLIMATIC ZCXSES.] 



METEOROLOGY. 



1199 



The varieties of climate may, as we have already seen, 

 arise from either of two causes latitude and elevatiou 

 j or from their conjoint influence. Thus, at the equator, 

 on the sea-level, we find an annual mean temperature of 

 about 80 ; but, ascending to a height of about 10,000 

 feet, we pass to a line of perpetual snow, equivalent to 

 the condition of the polar regions. Now between these 

 two extremes, it is found that, at every 2,000 feet, a zone 

 is obtained as we ascend, nearly corresponding in 

 productions with other zones, given by dividing the 

 interval between the equator and the poles into eight 

 parts, proceeding north or south from the equator. 

 The latitudinal zones can only be limited approxi- 

 mately, because of the irregular inflections of the 

 isothermal lines,* which rise towards the poles, or fall 

 nearer the equator, according to various local affecting 

 causes. The succeeding table, however, affords both the 

 latitudes and longitudes of the various places, having the 

 game yearly isothermal ; and any map may thus be used 

 in connection with the following observations, the line 

 being temporarily traced by the pencil, from place to 

 place, as required. To be explicit, we again remark, 

 that elevation and latitude may be considered as con- 

 vertible terms, in studying the distribution of living and 

 extinct creatures of both kingdoms. 



The following are the names of the zones, and 

 their approximate range in latitude, north or south 

 of the equator subject to the modification of local 

 cause*. 



1. Equatorial . . extending from to 15 lat. 



2. Tropical ... , 15 to 24 



3. Sub-Tropical . , 24 to 34 



4. Warm-Ten- perato , 34 to 45 



5. Cool-Temperate , 45 to 58 



6. Sub-Arctic . . , 58 to 67 



7. Arctic 67 to 75 



a Polar .... 75 to 90 (?) 



1. Commencing with the equatorial regions, wo find 

 a climate exceedingly hot and moist, and just that in 

 which vegetation has every circumstance favourable for 

 its full development. There grow in perfection, palms, 

 bananas, ginger, spices, gums, the beautiful water-lily 

 called the Victoria Regia, rafflesia, the sugar-cane, 

 coffee, dye-woods, cabinet woods, cotton, &c. 



2. At about 15 north or south of the equator the 

 tropical zone commences, and it extends to about 24 of 

 L-ititude. Tree-ferns, convolvuli, pepper, tropical fruits 

 of many kinds, the cocoa-nut, rice, coffee, sugar, dye- 

 woods, cabinet woods, indigo, spicea, gums, tobacco, and 

 cotton, are extensively grown. 



3. From 24 to 34, which includes India, North 

 Africa, the West Indies, &c., is the sub-tropical zone, 

 the productions of which much resemble the former ; 

 but there may be added opium and tea, up to 31 N. 

 This zone embraces the chief cotton-growing countries, 

 both in India and the United States, and also of tobacco 

 and sugar. The characteristic plant^ are the myrtle 

 tribe, magnolias, large forest-trees, rich flowering plants, 

 luscious fruits, date-palms, &c. 



4. From 34 to 45 constitutes the warm-temperate zone, 

 including Portugal, Spain, Greece, Italy, the south of 

 France, ifce. The vine, and the mulberry for the silk- 

 worm, are characteristic. The trees are the cork-tree, 

 oak, chesnut, beech, &c. ; the myrtle, heaths, <tc. The 



i!s flourish ; rice is grown in some parts ; amongst 

 fruits are oranges, lemons, nuts of many kinds, grapes in 

 great abundance for wine-making, or to bo sold dried as 

 raisins ; currants for drying, grown in Greece ; peaches, 

 kc. ; such taking the place of sub-tropical fruits, which 

 hero disappear. 



5. From 45 to 68 constitutes the cool-temperate 

 zone ; and the productions of our own country may, to 

 some extent, be taken as the type. Amongst trees are 

 the oak, elm, beech, ash, birch, &c. ; cereals grow 

 abundantly in the lower and middle latitudes ; grasses 

 also abound for pasture ; flax and hemp are cultivated ; 

 apples, pears, plums, cherries, &c., are the fruits; the 



Sec ante, p. 1194. 



grape not ripening so as to be fit for producing wine, 

 except in the lower division, where it is extensively pro- 

 duced. Great Britain, Ireland, Mid-France, Switzerland, 

 Prussia, Austria, &c., are in this zone ; and thus some of 

 the most civilised portions of the world are comprised 

 within its limits. In our country wheat will scarcely 

 grow in the extreme north ; hence oats and barley replace 

 it to a large extent in Scotland, and also in Norway, 

 Sweden, &c. The hop, ivy, honey-suckle, c., are 

 amongst the creeping plants, the two latter being common 

 in the forests. Moat of the colonised portions of Australia, 

 Tasmania, and New Zealand are within this zone, ill south 

 latitude ; and hence their vegetable products resemble 

 those of the countries in Europe, similarly situated in 

 north latitude ; but are varied by the presence of trees 

 peculiar to the Australian continent, such as the 

 Eucalyptus, or gum-tree, a kind of acacia, numerous 

 forest evergreens, tree-nettles, <fcc. 



6. In the sub- Arctic zone, from 58 to C7, the Conifercf 

 appear, and flourish well ; hence the large pine-forests in 

 Norway, and parts of North America which, however, 

 from being so much cooler than in the same latitudes in 

 Europe, have this kind of tree much nearer the equator. 

 There are also the birch, willow, alder, grasses ; rarely 

 wheat ; but oats, rye, and barley, lichens, and mosses. 



7 <fc 8. The Arctic zone, extending from 67 to 75 C , 

 gradually loses all trace of trees, which are replaced by 

 shrubs of rhododendra, bog-myrtle, lichens, and mosses ; 

 and, in the Polar zone, reaching hence to the poles, 

 saxifrage, ranunculi, cochleari.-c, and abundance of 

 lichens, mark the extreme limits of vegetative power. 



So far we have observed the distribution of plants, in 

 respect to latitude, north or south of the equator 

 taken certainly on an extremely broad and general scale ; 

 for some portions of the earth's surface must be entirely 

 omitted from any of the limits thus pointed out. Thibet, 

 for example, whilst nominally in the sub-tropical zone, 

 has really a climate almost, at times, resembling an 

 Arctic one ; but this is owing to its great elevation, of 

 which we shall presently have to speak more fully. The 

 Sahara desert, Arabia, much of Central Africa and 

 South America, equally afford exceptions, the nature of 

 which has been explained previously, t 



With respect to zones of altitude, similar allowances 

 have to be made, and for the same reasons. Commencing 

 at the sea-level at the equator, we shall have, of course, a 

 climate of the equatorial type, in which, up to a height 

 of 2,000 feet, palms, bananas, ginger, &c., flourish. 

 From 2,000 to 4,000 feet, the tree-ferns, &c., exist ; from 

 4,000 to 6,000 feet, myrtles, laurels, magnolias, heaths, 

 &c. ; from 6,000 to 8,000 feet, evergreens, olives, &o. ; 

 from 8,000 to 10,000 feet, oaks, beeches, &c. ; from 

 10,000 to 12,000 feet, firs, &c. (on Etna, so low as 7,000 

 feet, and in the Pyrenees, 5,500 feet) ; from 12,000 to 

 14,000 feet, rhododendra, and Alpine plants ; and from 

 14,000 to 16,000 feet, Arctic plants of various kinds, 

 mosses, and lichens in abundance the latter, as in hiyh 

 latitudes, being the last form of vegetation that is 

 met with. 



It would be beyond the scope of our present object if 

 wo were to enquire minutely into the specific differences 

 which subsist between the plants of the various zones, 

 and the relation which they have with the climate in 

 which any of them best flourish. This is a subject 

 which would require considerable botanical knowledge 

 on the part of our readers, and we should therefore have 

 to presume on an acquaintance with that science, which 

 has to bo treated in detail in the succeeding volume. 

 We may observe generally, however, that the existence 

 of a plant depends more essentially on the temperature of 

 any locality, than on the complete suitability of its food. 

 This, of some kind, it can generally find anywhere, to an 

 extent sufficient for bare existence, if not for luxuriant 

 growth ; but if the climate be too cold or hot, then many 

 plants will not even grow ; or, if they do, they never bear 

 fruit which will ripen. This is a matter of constant 

 experience, especially with the cereals, on which the food 

 of man so greatly depends, and the growth of which is 



ante, p. 1193. 



