38 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 69 



Sloanea quadrivalvis. Miconia fulva. 



Peltaa sessiliflora. Lantana camara. 



Sida jamaicensis. Cornutia pyramidata. 



Sida linifolia. Duranta plumieri. 



Guasuma ulmifolia, Guacimo. Diodia rigida. 



Curatella americana. Pedis elongata. 



Miconia rubiginosa. Pedis swartsiana. 



UPPER TROPICAL ZONE 



With the exception of the lofty Volcan de Chiriqui, the Upper 

 Tropical Zone embraces the slopes and crests of mountains above 

 3,000 to 8,500 feet altitude. Its upward extent on the Volcan de 

 Chiriqui has not been accurately determined, but probably reaches 

 on general slopes to near the 8,000-foot contour line or somewhat 

 higher. Practically the entire area is densely forested, but the 

 forest, largely of palms, is of somewhat smaller growth than in much 

 of the Lower Tropical Zone. While the zone as a whole is humid, no 

 very definite divisions on the basis of moisture being now recogniz- 

 able in Panama, variations in humidity due to slope exposure are 

 often marked. The northeast trade winds cause precipitation or 

 cloud formation, affecting the northern slopes of the mountains in 

 this zone during the so-called " dry " season. Fogs and generally 

 moist conditions extending across the summits reach about 500 feet 

 down the southern slope, below which their influence rapidly 

 diminishes, the altitude of the line of demarcation depending on that 

 of the crest. An extract from the itinerary of Mr. W. W. Brown, Jr., 

 quoted by Mr. Outram Bangs 1 is descriptive of this zone on the 

 Volcan de Chiriqui. It runs as follows : 



On the further side of the llano, at an altitude of 3,500 feet, the trail leaves 

 the plain and passes through valleys and over hills, in a cool luxuriant forest 

 with swiftly running streams and brooks rippling among fern-covered rocks. 

 One begins to see an immense number of birds, all of different species from 

 those of the lowlands — water ouzels dart about on the rocks in the foaming, 

 rushing streams, small thrushes (Catharus) and solitaires are singing every- 

 where in the jungle and the branches overhead are full of tanagers and 

 warblers. This Zone extends up to about 5,000 feet. Between 5,000 and 8,ooo 

 feet another change in the bird life is noticed, but not so marked a one. 



More complete knowledge of the 4,500 to 5,000 feet of altitudinal 

 extent assigned to this zone may point to the desirability of making 

 divisions which are not satisfactorily recognizable now. 



1 The Auk, Vol. 3, p. 17, Jan. 30, 1902. 



