78 ILLINOIS STATE ACADEMY OF SCIENCES 



country. The change in the character of the vegetation 

 is quite abrupt, and is noticeable especially between San 

 Jose and Punta-Arenas. Chemical content in the soil 

 here plays little or no role in the growth of plants; it 

 is mainly a matter of moisture. 



Permit me to mention another similar situation in 

 Guatemala. In southeastern Guatemala is a region lying 

 mainly along the Motagua River which is one of the 

 most notable deserts in all Central America. On either 

 side of the river is a range of mountains, off-shoots from 

 the Sierra Madre; their general course is almost north- 

 east and southwest, as is most of the mountain ranges 

 which make up the great Honduras-Nicaragua peninsula. 

 The prevailing winds here also are from the east or 

 southeast, and the precipitation is confined mainly to the 

 mountains east of the Motagua River or to the high 

 slopes of the mountains to the northwest of the river. 

 There is a very limited amount of precipitation in the 

 valley, and the result is a typical cactus desert miles in 

 extent, centering about the region of Zacapa and known 

 locally as the Zacapa desert. Farther northeast and at 

 lower altitudes in this same river valley where there is 

 little to obstruct the moist-laden trade winds, namely, in 

 the vicinity of Puerto Barrios, there is one of the most 

 luxuriant tropical palm-vegetations to be found any- 

 where in Central America. These may seem to be very 

 simple matters in ecology. They are; but they are sig- 

 nificant nevertheless, not only in determining the charac- 

 ter of vegetation on local areas but also in determining 

 the distribution of vegetation in the American tropics. 

 A particular opportunity, however, to which I should like 

 to call the attention of the ecologists is that of a study 

 of plant succession in volcanic craters. For example, 

 there are on Mount Poas in Costa Rica several volcanic 

 craters representing eruptions which have taken place 

 at different times, and each crater has, more or less, its 

 distinctive flora in accordance with its relative age. 



What now are the specific opportunities in Central 

 America for the plant geographer? No one can say at 

 present with any degree of certainty how far the Andean 

 flora of South America extends into Central America, 



