TERTIARY FLORA OF CHILE 107 



ical forms, nearly all of these genera contain species that 

 are not strictly confined to that environment. 



The modern Amazon basin flora, for example, presses up- 

 ward into the eastern Andes, where the limiting factors seem 

 to be precipitation, and ultimately of course temperature, to 

 a degree that is amazing when seen for the first time. The 

 transition upward in the montana zone is gradual, certain 

 types drop out, the same as they do in tracing the montana 

 flora southward in Bolivia beyond the equatorial zone. The 

 modern field botanist would not be misled, but the closet 

 botanist, as well as the paleobotanist, would be, and it would 

 be easily possible to collect scores of species in the Yungas 

 of Bolivia at an altitude of 8,000 feet in latitude 20, that 

 would be pronounced lowland tropical. 



Humboldt's classical zones of altitudinal vegetation may 

 hold good in the Eucadorian Andes, although I much doubt 

 it they certainly do not hold in Peru or Bolivia where many 

 so-called tropical forms reach altitudes of over 11,000 feet. 



The montana flora of eastern Peru and Bolivia continues 

 southward to about 25 South, with the dropping out of 

 some forms and reduction in the number of lianes and 

 epiphytes, and this so-called tropical forest continues on 

 southward with some modifications along the Andes into the 

 Argentine provinces of Oran and Tucuman to between 27 

 and 28 South. The flora of the latter region, although dif- 

 ferent in many features, is the nearest geographical approach 

 of a similar modern flora to the Chilean region. 



This flora contains such types as Machserium, Myrsine, 

 Chorisia, Nectandra, Cupania, Cedrela, Acacia, Eugenia, 

 Terminalia, Schmidelia, Ruprechtia, Erythroxylon, Randia, 

 Pisonia, Canavalia, Desmodium, Heteropteris, Serjania, etc. 

 the last four being lianes. 



Ecologists will think of many limiting factors other than 

 those of mean annual temperatures and rainfall, which are the 

 two that seem most obvious, for example low maximum sum- 

 mer temperatures because of cloudiness may be an important 



