PHYSIOGNOMY OF PLANTS. 241 



rescent heaths, like some other African plants, extend to the northern 

 shores of the Mediterranean : they adorn Italy, and the cistus-covered 

 grounds of the south of Spain. The declivity of the Peak of Tene- 

 riffe is the locality where I have seen them growing with the greatest 

 luxuriance. In the countries adjoining the Baltic, and farther to 

 the north, the aspect of this form of plants is unwelcome, as an- 

 nouncing sterility. Our heaths, Erica (Calluna) vulgaris, Erica 

 tetralix, E. carnea, and E. cinerea, are social plants, and for centuries 

 agricultural nations have combated their advance with little success. 

 It is remarkable that the extensive genus which is the leading repre- 

 sentative of this form appears to be almost limited to one side of 

 our planet. Of the 300 known species of Erica only one has been 

 discovered across the whole extent of the New Continent, from 

 Pennsylvania and Labrador to Nootka and Alashka. 



The Cactus form, ( 20 ) on the other hand, is almost exclusively 

 American. Sometimes spherical, sometimes articulated or jointed, 

 and sometimes assuming the shape of tall, upright, polygonal 

 columns resembling the pipes of an organ, this group presents the 

 most striking contrast to those of Liliacese and Bananas. It com- 

 prises some of the plants to which Bernardin de St. Pierre has ap- 

 plied the term of "vegetable fountains in the desert." In the 

 waterless plains of South America, the animals suffering from thirst 

 seek the melon-cactus, a spherical plant half buried in the dry sand, 

 and encased in formidable prickles, but of which the interior abounds 

 in refreshing juice. The stems of the columnar cactus rise to a 

 height of 30 or 32 feet; they are often covered with lichens, and, 

 dividing into candelabra-like branches, resemble, in physiognomy, 

 some of the Euphorbias of Africa. 



While the above-mentioned plants nourish in deserts almost de- 

 void of other vegetation, the Orchidese ( 21 ) enliven the clefts of the 

 wildest rocks, and the trunks of tropical trees blackened by excess 

 of heat. This form (to which the Vanilla belongs) is distinguished 

 by its bright green, succulent leaves, and by its flowers of many 

 colors and strange and curious shape, sometimes resembling that of 

 winged insects, and sometimes that of the birds which are attracted 

 by the perfume of the honey vessels. Such are their number and 

 variety, that, to mention only a limited district, the entire life of a 

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