GEOGRAPHICAL DISTRIBUTION OF PLANTS. 



169 



are the forests which cover the plains of South 

 America between the Orinoco and the Amazons, 

 that were it not for intervening rivers, the 

 monkeys, almost the only inhabitants of these 

 regions, might pass along the tops of the trees 

 for several hundred miles together without 

 touching the earth." This vast wilderness pre- 

 sents none of that wearisome uniformity of as- 

 pect which often characterises the forests and 

 heaths of temperate climates. Not only do we 

 meet in the tropical regions with nervr genera a,ndi 

 specieSjhuivrVAinswf families of plants, strongly 

 contrasted in their forms and modes of growth 

 with those of other parts of the world : others 

 again acquire, in the torrid zone, the height and 

 bulk of trees, which in Europe never exceed 

 the magnitude of herbs; and some of those which 

 abound in our climates wholly disappear. 



Yet the mean annual temperature of the equa- 

 torial regions is by no means so difiFerent from that 

 of other parts of the globe as we might be led 

 to suppose by observing the extraordinary phe- 

 nomena of tropical vegetation. In a climate 

 where the bamboo attains in a few months to 

 the height of sixty feet; where the whole aspect 

 of the vegetable world exhibits so singular and 

 striking an aspect, we naturally expect to find 

 as marked an increase in the heat of the sun's 

 rays. This, however, is not the case. There is 

 no reason to believe that the mean temperature 

 at the equator exceeds 82°, a degree of warmth 

 by no means very uncommon in our own coun- 

 try. The mean temperature of Cumana, on 

 the northern coast of South America, in latitude 

 10° 27', is 82°; that of Havannah, the capital of 

 the island of Cuba, in latitude 23°10',is 78°; that 

 or" Madras, in latitude 13° 5', is 81°; that of 

 Manilla, the principal of the Philippine islands, 

 in latitude 15°, is 78°. In fact, the climate of 

 most parts within the tropics is more remarkable 

 for equability than for extreme heat. Twice in 

 the year the sun is vertical to every place lying 

 within the torrid zone; therefore every place so 

 situated should have two summers in twelve 

 months, and of course two winters. But, in 

 fact, the difference of temperature at different 

 seasons is so trifling in these regions, as scarcely 

 to attract attention : at Cumana, for instance, 

 the mean temperature of the winter is 80^°; 

 that of the three hottest months only 885°. 

 The different seasons are marked by circum- 

 stances far more striking than this slight differ- 

 ence of temperature. Prom the time when the 

 sun becomes vertical in its passage towards the 

 tropic till it again becomes vertical in returning 

 towards the equator, (that is, during the time 

 answering to summer in the temperate zone,) 

 the country, in most parts of the tropical regions, 

 is deluged with almost continual rain, while 

 the other part of the year is a season of fine 

 weather. 



A similar equability of climate is found to pre- 

 vail in those districts which are situated far above 

 the level of the sea, but of course accompanied 

 by a lower temperature. Thus the mean tem- 

 perature of Quito, directly under the equator, 

 at a height of eight thousand feet, corresponds 

 nearly with that of the south of France; but 

 the lowest point which the thermometer has 

 been observed to indicate at Quito is 42° ; whereas 

 at Marseilles, though the climate there is less 

 liable to great fluctuations than in most places 

 under the same latitude, the mercury sinks oc- 

 casionally as low as 23°. The temperature of 

 that great elevated plain which occupies the 

 western side of the continent of South America, 

 resembles a perpetual spring; and as very little 

 difference is felt in the warmth of the different 

 seasons, the gradual diminution of heat from 

 the level of the sea upwards is more distinctly 

 observable than in other climates. Accordingly, 

 the several families of plants which cover the 

 sides of the Andes are arranged in distinct belts 

 or zones, whose limits are marked with a pre- 

 cision unknown in the mountains of Europe, 

 where the plants belonging to the plains are 

 sometimes seen growing in company with those 

 of more elevated regions. Upon the declivities 

 of the South American mountains may be found, 

 within a comparatively small compass, every 

 gradation of temperature, from that of the 

 burning plains at their feet to the limits of per- 

 petual snow; and every variety of vegetable 

 productions, from the palms and bamboos, sugar- 

 canes and plantains, to the mosses and lichens 

 which clothe the rocks thirteen thousand feet 

 above. 



There are some families of plants which arrive 

 in the tropical regions at a magnitude unknown 

 in our climate, as the grasses, ferns, and mallows. 

 The bamboo, which has a jointed hollow stalk 

 like the grasses, often reaches the height of sixty 

 feet. Of ferns we have in England about forty 

 species, none of which exceed three or four feet 

 in height; whereas in the torrid zone they attain 

 the size of trees. Of all the forms of tropical 

 vegetation, these and the bamboos, according to 

 Humboldt, most excite the attention, and 

 awaken the admiration of the traveller, in 

 their general aspect the tree ferns resemble the 

 palms. Their stems are generally black, as if 

 burnt with the sun; their leaves of a bright and 

 delicate green, beautifully crisped at the edge. 

 It has been observed of the ferns that they prin- 

 cipally delight in insular situations; few com- 

 paratively are found in the interior of laige 

 continents, owing, perhaps, to the want of a 

 due proportion of moisture. They abound 

 amongst the dropping springs that ooze from the 

 crevices of rocks; and some species of exquisite 

 beauty are found lining the sides and roof of 

 the little caverns which contain the sources of 



