PHYSIOGNOMY OF PLANTS. 225 



The temperate zone in our old continent unfortunately is 

 wholly devoid of the delicately pinnate Mimosas (18), whose 

 predominating forms are Acacia, Desmanthus, Gleditschia, 

 Porleria, and Tarnarindus. This beautiful form occurs in the 

 United States of North America, where, under equal parallels 

 of latitude, vegetation is more varied and luxuriant than in 

 Europe. The Mimosas are generally characterised, like the 

 Italian pine, by an umbellate expansion of their branches. 

 An extremely picturesque effect is produced by the deep blue 

 of a tropical sky gleaming through the delicate tracery of 

 their foliage. 



Heaths (19), which more especially belong to an African 

 group of plants, include, according to physiognomic cha- 

 racter and general appearance, the Epacridece and Diosmese, 

 many Proteaceae, and the Australian Acacias, which have no 

 leaves but mere flattened petioles (phyllodia). This group bears 

 some resemblance to acicular-leaved forms, with which it 

 contrasts the more gracefully by the abundance of its cam- 

 panulate blossoms. The arborescent heaths, like some few 

 other African plants, extend as far as the northern shores of 

 the Mediterranean. They adorn the plains of Italy, and the 

 Cistus groves of southern Spain, but I have nowhere seen them 

 growing more luxuriantly than on the declivities of the Peak 

 of Teyde at Teneriffe. In the countries bordering on the 

 Baltic, and further northward, the appearance of this form of 

 plants is regarded with apprehension, as the precursor of 

 drought and barrenness. Our heaths, Erica ( Calluna) vulgaris, 

 and Erica tetralix, E. carnca and E. cinerea, are social plants, 

 against whose extension agricultural nations have contended 

 for centuries, with but little success. It is singular that the 

 principal representative of this family should be peculiar to 

 one side of our planet alone. There is only one of the three 

 hundred known species of Erica to be met with in the new 

 continent, from Pennsylvania and Labrador to Nootka Sound 

 and Alaschka. 



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