PHYSIOGNOMY OF PLANTS. 227 



Africa, the Peruvian Collet hi, and the Siberian Calligonum 

 Pallasia, are nearly allied to the form of the Casuarinas. 



While the Banana form presents us with the greatest degree 

 of expansion, the Casuarinas and the acicular-leaved (23) 

 trees exhibit the greatest contraction of the leaf-vessels. 

 Pines, Thujas, and Cypresses constitute a northern form but 

 rarely met with in the tropics and in some conifera3 (Dammara 

 Salisburia), the leaves are both broad and acicular. Their ever- 

 green foliage enlivens the gloom of the dreary winter land- 

 scape, while it proclaims to the natives of the polar regions 

 that, although snow and ice cover the surface, the inner 

 life of plants, like the Promethean fire, is never wholly ex- 

 tinct on our planet. 



Besides the Orchideae, the Pothos tribe of plants (24) also 

 yields a graceful covering to the aged stems of forest trees in 

 the tropical world, like the parasitic mosses and lichens of our 

 own climes. Their succulent herbaceous stalks are furnished 

 with large leaves, arrow-shaped, digitate, or elongated, and 

 invariably furnished with thick veins. The blossoms of the 

 Aroidese are inclosed in spathes, by which their vital heat is 

 increased; they are stemless, and send forth aerial roots. 

 Pothos, Dracontium, Caladium, and Arum are all kindred 

 forms ; and the last-named extends as far as the coasts of the 

 Mediterranean, contributing, together with succulent Tussi- 

 lago (Coltsfoot), high thistles, and the Acanthus, to give a 

 luxuriant southern character to the yegetatiou of Spain and 

 Italy. 



This Arum form is associated, in the torrid regions of South 

 America, with the tropical Lhines or creeping plants (25), 

 which exhibit the utmost luxuriance of vegetation in Paulli- 

 nias, Banisterias, Bignonias, and Passion-flowers. Our ten- 

 drilled hops and vines remind us of this tropical form. On 

 the Orinoco the leafless branches of the Bauhinia are often 

 upwards of 40 feet in length, sometimes hanging perpen- 

 dicularly from the summit of lofty Swietenioe, (Mahogany 



Q2 



