PLIOCENE PISLLYPAMPA BOLIVIA 153 



tis. The three ferns represent the two families Polypodiaceae 

 and Gleicheniaceae, and all three are familiar types of the 

 Yungas region of Bolivia at the present time. The mono- 

 cotyledons represent the two striking and familiar types of 

 the South American tropics the wild banana (Heliconia) 

 and the Iriartea palm (Iriartites). 



The dicotyledons comprise the eight orders Urticales, 

 Chenopodiales, Ranales, Resales, Geraniales, Thymeleales, 

 Myrtales and Ebenales, and possibly the Sapindales. The 

 largest of these orders is the Rosales with four species of 

 Mimosaceae and Caesalpiniaceae and the Geraniales with one 

 species each of the four families Rutaceae, Burseraceae, Hum- 

 iriaceae and Meliaceae. There are two species of Sapotaceae 

 and one each of the families Moraceae, Nyctaginaceae, Anon- 

 aceae, Lauraceae, Myrtaceae, and possibly the Sapindaceae. 



The genera of dicotyledons represented are Coussapoa, 

 Pisonia, Anona, Cassia, Pithecolobium, Pilocarpus, Saccog- 

 lottis, Protium, Mespilodaphne, Myrcia, Sideroxylon, Chry- 

 sophyllum, and Cedrela or Sapindus. All of these are char- 

 acteristic forms of the warmer parts of South America. The 

 fossil flora is essentially modern in facies ana typically South 

 American. The accompanying table shows the most closely 

 related existing species with their occurrence and habitat. 



The modern species most similar to the fossil forms where 

 these can be definitely ascertained and located geographically, 

 occupy regions where the rainfall varies between 20 and 80 

 inches per annum. The majority of these exist under con- 

 ditions approaching this maximum more nearly than the 

 minimum. This is shown not only by the genera that are 

 represented, but by the individual character of the leaves, 

 some of which are large in size and mesophytic in structure, 

 thus denoting humid conditions. Moreover they are nearly 

 all types which extend to regions which experience a summer 

 and fall rainy season, and a dry winter and spring during 

 which many of the trees shed their leaves. Great observed 

 variation in this respect depends upon the particular situ- 



