132 AGRICULTURAL ECONOMICS 



rate of evaporation and thus enlarges the demand for rainfall to 

 satisfy the farmer's crops. Finally, "heat rigor" is as real a draw- 

 back as the checking of growth by cold. That is, there is a maximum 

 temperature which any given species of plants can tolerate, and this 

 marks the upper limit of its possibilities of growth. Even before this 

 point is reached, growth may be distinctly retarded a condition 

 familiar to all through its manifestation upon plant life in the hottest 

 period of summer weather. 1 



The handicap of the tropics is well portrayed by Professor Ells- 

 worth Huntington in a recent article on Guatemala.* He says: 



We are apt to think of tropical lands as places where vegetation is 

 exuberant and where a living is obtainable with extreme ease. As a matter 

 of fact, in vast portions of the torrid zone it is harder to get a living than 

 in the temperate zone. In the true tropical forest, agriculture is practically 

 out of the question. Even for the white man it is difficult to clear the 

 ground, and for the sluggish son of the tropics it is almost impossible. 

 In the tropical rain forest bushes will grow to a height of ten to twenty 

 feet in a single year. Indeed, in the short space of two months so much 

 herbage will spring up that a piece of forest which has been cut cannot be 

 burned, even though the trees have become dry. 



This is not theory, but actual fact. In the spring of 1913, in a part of 

 Guatemala where the forest is by no means of the densest kind, and where 

 a considerable number of coffee plantations exist, I saw this happen. The 

 trees had been cut, but so many showers fell during the nominal dry season 

 that the branches did not become dry enough to burn, and consequently 

 many people were unable to plant crops. One might ask why they could 

 not plant old fields cleared in previous years. The answer is simple. In 

 this particular region the staple product is Indian corn. The first year 

 after new land has been burned it gives a splendid crop; but if the same 

 tract be planted a second time, the crop is so poor as not to be worth 

 raising. Just why this is so is not certain; perhaps because the abundant 

 rains leach out certain elements of the soil very rapidly; perhaps because 

 the warm, humid conditions of the ground develop toxic substances inimical 

 to cultivated plants; or perhaps because the heat of the sun causes the soil 

 to decompose with great rapidity, and hence quickly to lose its strength. 

 At any rate, the fact remains that it seems to be impossible to cultivate the 

 same tract more than one year at a time. The ordinary practice 'is to 

 clear and burn an area, plant it a single year, then leave it to grow up to 

 bushes for from three to five or ten years, and then, when the soil has 



1 See E. Davenport, Principles of Breeding, pp. 255-57. (Ginn & Co.) 

 3 Yale Review, April, 1914, p. 506. 



