180 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, No. 9 
overgrown with tropical vegetation. The outlook from the high 
pyramids in all directions is an undulating, unbroken forest. The 
present conditions are to be considered as a result of reforestation, not 
only of the sites of the cities, but probably of the whole surrounding 
region. It is a regular consequence of the primitive system of agri- 
culture to reduce a forest country to an open, fire-swept grassland.! 
Though tropical forests are restored rapidly in small clearings, the 
reforestation of an extensive grassland necessarily is very gradual, with 
a long succession of different conditions and types of trees to be 
established and replaced before there can be a complete return to the 
original state of the undisturbed, or “virgin forest.” Some elements 
of the forest flora come in very slowly, even after apparently favorable 
conditions have been established. Thus there may be new forests 
with no palms in the undergrowth, though several kinds of palms may 
be found in older forests near by. In more advanced stages of refor- 
estation palms may be abundant, but represent only a few species, 
which is true of the forests of Petén. 
The rapid destruction of the ancient cities by the forest, now to be 
witnessed in the Petén region, is evidence against the idea of very 
great antiquity, estimated by some archaeologists in thousands of 
years. In view of the damage now being done by the growth and 
uprooting of large trees, it does not appear that many centuries will be 
required to reduce all of the massive structures to shapeless mounds. 
The destruction tends, no doubt, to accelerate as the soil deposits 
accumulate among the loosened stones and the trees grow to larger 
size before uprooting. Several centuries may have passed after the 
cities were abandoned before they were covered by the forest. The 
dates that have been deciphered from the sculptured monuments are 
from a period corresponding to the early centuries of the Christian 
Era, though doubtless the city-building age was preceded by a long 
period of agricultural development. The Maya system of chronology 
used in dating the monuments would go back to about 3500 B.C. 
The new palm would not be classified ecologically with the under- 
growth species, but as a true forest type, growing to the same height 
as many other trees. It has a rather slender trunk, about 6 inches in 
1See ‘“Milpa Agriculture, A Primitive Tropical System,’’ Smithsonian Report for 
1919, pp. 307-326. 
*Of the undergrowth species an Acanthorhiza is by far the most abundant, two 
species of Chamaedorea (C. elegans and ernesti-augusti) are common, and three others 
of occasional occurrence. ‘Two large forest palms are also very common in some locali- 
ties, Alialea cohune and a very tall, slender palmetto, locally known as botén. The 
taciste palm, a species of paurotis, grows in open places and survives burning over. 
