136 Bulletin American Museum of Natural History. [Vol. XXXVI, 



both Tropical Zone and even Temperate Zone species whose habits fit them 

 to life in more or less open, bushy places. Such an association was found 

 at Quetame (alt. 4500 ft.) in the Eastern Andes, where in the scanty growth 

 of low trees bordering the Rio Negro and its tributaries we found Xanthoura 

 yncas cyanodorsalis, Schistochlamys atra and Thraupis episcopus leucoptera, 

 while in the immediately adjoining fields was Stm-nell^jnagnajn^dicmaMs, 

 and in bordering hedgerows, Semimenda gigas gigas and Brachyspiza capensis 

 peruviana. 



Usually, however, the Subtropical Zone is as clearly defined as the condi- 

 tions to which it owes its characteristic features. It is pre-eminently a 

 zone of forests, the product of the heavy rainfall and high degree of humidity 

 prevailing at the altitude in which the Subtropical Zone is found. 



In the field, we termed it the 'Cloud Zone,' so closely does its lower 

 border coincide with the height to which clouds descend on the mountain- 

 sides. This term, however, may be also applied to the two upper zones, 

 Temperate and Paramo, though cloud forests exist only in the Subtropical 

 and Temperate Zones, the temperature of the Paramo Zone being evidently 

 too low to permit of forest growth. Furthermore, the rainfall decreases 

 as the altitude increases. 



The forests of the Subtropical Zone, particularly on windward slopes, 

 present a luxuriance of growth not equalled even in the Tropical Zone. The 

 lower zone produces nobler, taller trees (we saw nothing in the subtropics 

 to approach the ceibas of the basal zone), but in profusion of undergrowth, 

 of parasites and epiphytes which thrive in this region of clouds, the Sub- 

 tropical Zone excels. It is the zone in which we found tree ferns attaining 

 their maximum height of approximately fifty feet, in which a climbing 

 bamboo grows in impenetrable tangles, in which orchids, bromelias and 

 plants of similar habit occupy every available point of vantage, clustering 

 thickly on the limbs and even trunks of trees; while every spot not occupied 

 by some other form of plant-life, is cushioned with moss. From each leaf 

 and limb water is constantly dripping, the bromelias are usually full to 

 overflowing, the moss is like a saturated sponge. Even when, at intervals, 

 the sun penetrates the clouds, the falling drops suggest a shower. 



In view of the altitude attained by the Subtropical Zone, far higher 

 mountains are required to act as effective barriers to its extension across 

 the ranges on the slopes of which it lies. This fact, in connection with the 

 exceptional continuity of the Subtropical Zone forests, gives to the life of 

 this zone a uniformity which, when one considers its length and the distance 

 which its arms are sometimes separated, is surprising. 



Latitudinally, the Subtropical Zone extends from central Venezuela 

 and Mexico at the north southward through Colombia to western Ecuador 



