194 PHYSIOGNOMY OF PLANTS. 



so are Willows, the different species of Pines, and Oaks, no 

 less widely disseminated : the latter (oaks) being always 

 alike in their fruit, though much diversified in the forms of 

 their leaves. In Willows, the similarity of the foliage, of the 

 ramification, and of the whole physiognomic appearance, in 

 the most different climates, is unusually great, almost greater 

 than even in Coniferse. In the southern part of the tem- 

 perate zone of the northern hemisphere the number of species 

 of willows decreases considerably, yet (according to the Flora 

 atlantica of Desfontaines) Tunis has still a species of its own 

 resembling Salix caprea ; and Egypt reckons, according to 

 Forskal, five species, from the catkins of whose male flowers 

 a medicine much employed in the East, Moie chalaf (aqua 

 salicis) is obtained by distillation. The Willow which I saw 

 m the Canaries is also, according to Leopold von Buch and 

 Christian Smith, a peculiar species, common however to that 

 group and to the Island of Madeira, S. canariensis. 

 Wallich's Catalogue of the plants of Nepaul and of the 

 Himalaya cites from the Indian sub-tropical zone thirteen 

 species, partly described by Don, Roxburgh, and Lindley. 

 Japan has its indigenous willows, one of which, S. japonica 

 (Thunb.) is 'also found as a mountain plant in Nepaul. 



Previous to my expedition, the Indian Salix tetrasperma 

 was the only known intertropical species, so far as I am 

 aware. We collected seven new species, three of which 

 were from the elevated plains of Mexico, and were found to 

 extend to an elevation of 8000 (about 8500 English) feet 

 above the level of the sea. At still greater elevations, for 

 example, on the mountain plains situated between 12000 



