INFLUENCE OF HEAT ON PLANTS. 75 



for them ; inasmuch as these species can no more flourish at the Equa- 

 tor, than the equatorial species can in these Temperate regions. And 

 such new supplies, adapted to new conditions, recur perpetually as we 

 advance towards the apparently frozen and untenantable regions in the 

 neighbourhood of the Pole. Every zone has its peculiar vegetables ; 

 and while we miss some, we find others making their appearance, as if 

 to replace those which are absent. 



104. Thus in the countries lying near the Equator, the vegetation 

 consists in great part of dense forests of leafy evergreen trees, Palms, 

 Bamboos, and Tree-Ferns, bound together by clustering Orchidse and 

 strong creepers of various kinds. There are no verdant meadows, such 

 as form the chief beauty of our temperate regions ; and the lower orders 

 of Vegetation are extremely rare. It is only in this torrid zone that 

 Dates, Coffee, Cocoa, Bread-fruit, Bananas, Cinnamon, Cloves, Nut- 

 megs, Pepper, Myrrh, Indigo, Ebony, Logwood, Teak, Sandal-wood, 

 and many others of the vegetable products most highly valued for their 

 flavour, their odour, their colour, or their density, come to full perfec- 

 tion. As we recede from the Equator, we find the leafy evergreens 

 giving place to trees with deciduous leaves ; rich meadows appear, 

 abounding with tender herbs ; the Orchidese no longer find in the atmo- 

 sphere, and on the surface of the trees over which they cluster, a suffi- 

 ciency of moisture for their support, and the parasitic species are re- 

 placed by others which grow from fleshy roots implanted in the soil ; 

 but aged trunks are now clothed with Mosses : decayed vegetables are 

 covered with parasitical Fungi ; and the waters abound with Confervas. 

 In the warmer parts of the temperate regions, the Apricot, Citron, 

 Orange, Lemon, Peach, Fig, Vine, Olive, and Pomegranate, the Myrtle, 

 Cedar, Cypress, and Dwarf Palm, find their congenial abode. These 

 give place, as we pass northwards, to the Apple, the Plum, and the 

 Cherry, the Chestnut, the Oak, the Elm, and the Beech. Going fur- 

 ther still, we find that the fruit trees are unable to flourish, but the tim- 

 ber-trees maintain their ground. Where these last fail, we meet with 

 extensive forests of the various species of Firs ; the Dwarf Birches and 

 Willows replace the larger species of the same kind ; and even near or 

 within the Arctic circle we find large flowers of great beauty, the 

 Mezereon, the yellow and white Water-Lily, and the Globe-flower. 

 Where none of these can flourish, where trees wholly disappear, and 

 scarcely any flowering-plants are to be met with, an humbler Cryptoga- 

 mic vegetation still raises its head, in proof that no part of the Globe is 

 altogether unfit for the residence of living beings, and that the empire 

 of Flora has no limit. 



105. But distance from the Equator is by no means the only element 

 in the determination of the mean temperature of a particular spot, and 

 of the vegetation which is congenial to it. Its height above the level 

 of the sea is equally important ; for this produces a variation in the 

 amount of heat derived from the Sun, at least as great as that occa- 

 sioned by difference of latitude. Thus it is not alone on the summits 

 of Hecla, Mount Blanc, and other mountains of Arctic or temperate 

 regions, that we find a coating of perpetual snow ; we find a similar 

 covering on the lofty summits of the Himalayan chain, which extends 



