146 The Naturalist in Nicaragua 
not because of any change in the nature of the soil or bed- 
rock. It cannot be for lack of moisture, for around Libertad 
it rains for at least six months out of the twelve. The surface 
of the ground :is not level on the savannahs, but consists of 
hill and dale, just as in the forest. Altogether the conditions 
seemed to be exactly the same, and it appeared a difficult 
matter to account for the fact that the forest should end at 
an irregular but definite line, and that at that boundary 
grassy savannahs should commence. After seeing the 
changes that were wrought during the four and a half years 
that I was in the country, I have been led to the conclusion 
that the forest formerly extended much further towards the 
Pacific, and has been beaten back principally by the agency 
of man. The ancient Indians of Nicaragua were an agri- 
cultural race, their principal food then, as now, being maize; 
and in all the ancient graves, the stone for grinding corn is 
found placed there, as the one thing that was considered 
indispensable. They cut down patches of the forest and 
burnt it to plant their corn, as all along the edge of it they 
do still. The first time the forest is cut down, and the ground 
planted, the soil contains seeds of the forest trees, which, 
after the corn is gathered, spring up and regain possession 
of the ground, so that in twenty years, if such a spot is left 
alone, it will scarcely differ from the surrounding untouched 
forest. But it does not remain unmolested. After two or 
three years it is cut down again and a great change takes 
place. The soil does not now contain seeds of forest trees, 
and in their stead a great variety of weedy-looking shrubs, 
only found where the land has been cultivated, spring up. 
Grass, too, begins to get a hold on the ground; if it prevails, 
the Indian, or Mestizo, does not attempt to grow corn there 
again, as he knows the grass will spoil it, and he is too indolent 
to weed it out. Often, however, the brushwood has been cut 
down and burnt, and fresh crops of corn grown several times 
before the grass has gained such an advantage that the 
cultivator gives up the attempt to plant maize. There is 
then a struggle between the weedy shrubs and the grass. The 
leaf-cutting ants come to the aid of the latter. Grass they 
will not touch, excepting to clear it away from their paths. 
The thick forest they do not like, possibly because beneath 
its shade the ground is kept too damp for their fungus beds. 
