51 



Taking first the region within the lee of the Maestra, we have 

 two main factors that must be taken into account in any attempt 

 to understand the regional distribution of the plant groups ; and 

 these are the practical stability of the temperature and rainfall, 

 and the great instability and inequality of available surface- or 

 drainage-water. With these in mind we may enumerate several 

 variations in the plant associations that are directly traceable to 

 one or both of these factors. Other factors, such as soil, which 

 throughout the region is a decomposition of the native granite, 

 and light, which does not vary enough to make much difference, 

 may for the time be ignored. There seems little doubt that both 

 of these agencies are equally potent in all situations, and are not 

 therefore violent causes of variation. On this southern exposure 

 the three following characteristic areas may be enumerated : 



Slopes and Ridges 



These are covered with a dense growth of trees. The actual 

 number of species is not very great but the number of individuals 

 is enormous. In the expedition some hundred and fifty species 

 were noted, and, allowing for others that were overlooked, this 

 vast tract is covered almost exclusively with this arboreal vege- 

 tation. The number of individuals of the lower shrubs and her- 

 baceous plants is not accurately determinable, but it is very 

 small, so small that it can be almost truly said that these slopes 

 and ridges are without undergrowth. An appended list of the 

 collections from one such slope will give some idea of these 

 conditions : 



LitobrocJiia dentiadata Pithecolobium arboreiini 



Oplismenus hirtellus Lysiloma Sabicu 

 Arthrostylidium capUlifolium Lonchocarpus sericeus 



Pharus latifolius Bursera Simaruba 



Tillandsia fasciadata Swietenia Mahagoni 



Renealmia occidentalis Cedrela odorata 



VanUla pliaeantha . Dry petes lateriflora 



Cecropia sp. Spondias lutea 



Pisonia acideata Carpodiptera cubensis 



Oxa7idra virgata Calyptranthes sp. 



