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Azores, and in the north-west of Africa, a great 

 number of species, and even of genera, are pe- 

 culiar to Teneriffe, to Porto Santo, and Madei- 

 ra. Such are the mocanera, the plocama, the 

 bosea, the canarina, the drusa, and the pittos- 

 porum. A form which may be called northern, 

 that of the cruciform plants is already much 

 rarer in the Canaries, than in Spain and in Greece. 

 Still farther to the south, in the equinoctial 

 regions of both continents, where the mean tem- 

 perature of the air rises above twenty-two de- 

 gress, the cruciform plants are scarcely ever to 

 be seen. 



A question highly interesting to the history of 

 the progressive display of organization on the 

 Globe has been very warmly discussed in our 

 own times, that of ascertaining whether the po- 

 lymorphous plants are more common in the 



very old trunks of it ; but it was doubtful whether it was indi- 

 genous, or imported into this part of our continent. In re- 

 flecting on the migrations of plants, and on the geological 

 possibility, that lands sunk in the ocean may have heretofore 

 united Portugal, the Azores, the Canaries, and the chain of 

 Atlas, we conceive, that the existence of the rayrica faya in 

 western Europe is a phenomenon at least as striking as that 

 of the pine of Aleppo would be at the Azores. 



* Among the small number of cruciform species contained 

 in the Flora of Teneriffe, we shall here mention cheiranthus 

 longifolius, l'Herit. j ch. fructescens, Vent. ; ch. scoparius, 

 Brouss. ; erysimum bicorne, Aiton ; crambe strigosa, and c. 

 laevigata, Brouss. 



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