554 



ROOT CROPS 



RUBBER 



wall to the ceiling is a double-boarded partition, 

 and a door leads from the main cellar into this 

 smaller room. This is for keeping celery banked in 

 sand. The room has two small ventilators in the 

 roof. In the main room are bins and shelves for 

 different vegetables. The cellar is thirty-nine feet 

 six inches long, and twenty-six feet six inches 

 wide. The interior height is seven feet six inches. 

 The cellar is cool and dry, capable of being kept at 

 a uniform temperature, and will accommodate four 

 thousand bushels. 



RUBBER, OR CAOUTCHOUC. Figs. 790-798. 



By H. N. Ridley and J. H. Hart. ;! 



Rubber, or caoutchouc, is obtained from the 

 milky juice or latex of a considerable number of 

 trees and shrubs, erect or climbing, which inhabit 

 almost exclusively tropical parts, though some are 

 found in sub-tropical regions. These plants belong 



Fig. 790. A plantation of Bevea Brasiliensis and Oastilloa elaeUca. 

 Seven years old. 



to the families Urtieaeece, Euphorbiacem and Apoey- 

 nacecB. For practical agriculture, however, there 

 are only four of these plants which can be utilized 

 in cultivation, viz., Hevea Brasiliensis and Manihot 

 Glaziovii of the Euphorbiacem, and Castilloa elastica 

 and Fi£us elastica of the Urtieaeece. The big woody 

 climbers, Landolphia and Willughbeia, of the forests 

 of Africa and Malaya, do not respond to cultural 

 treatment. Hancornia and various species of Ficus 

 not mentioned above have given such poor results 

 under cultivation that they are not worth the at- 

 tention of the agriculturist, though the rubber has 

 value when it can be collected in sufficient quantity. 

 Mimusops globosa, a tree which produces "Balata 

 rubber " (or gutta-percha), is indigenous to South 

 America and the British island of Trinidad, and 

 might be cultivated to any extent. It is a slow- 

 growing tree, but to those who can afford to wait 

 it would doubtless be a most profitable investment. 

 In the four species above mentioned, we have 

 plants of which one or another is suitable for 



cultivation on a large scale and with good profit 

 very widely in the tropical regions. All are trees 

 of considerable size, and, under suitable circum- 

 stances, of rapid growth. 



The United States is entirely dependent on 

 imports for its rubber. Crude rubber is the third 

 largest of the tropical imports of this country. 

 The imports for the five years, 1898-1902, were as 

 follows : 



1898 $25,386,010 



1899 31,707,630 



1900 31,376,867 



1901 28,455,383 



1902 24,899,230 



Average ............ 28,365,024 



It is absolutely essential for the agriculturist 



who intends planting rubber trees, first carefully to 



select the kind suited for the climate and soil in 



which he intends to plant. Much money has been 



wasted by attempting to plant Ceara 



rubber in the tropical rain-forest region. 



Such errors are easily avoidable. 



The latex. 



The latex, or milk, is a white liquid 

 consisting of water containing proteid 

 matter, sugar and minute globules of 

 caoutchouc or rubber. The art of mak- 

 ing the rubber consists in separating the 

 rubber from the water and other con- 

 stituents of the latex. 



The latex occurs in a series of special 

 vessels (the laticiferous vessels) which 

 permeate the bark of the stem and twigs 

 and also the leaves and other soft parts 

 of the trees. A section of the bark of 

 the Para rubber (Hevea) under the mi- 

 croscope shows on the outer surface sev- 

 eral layers of hard, thick-walled cells, 

 forming the cork layer ; below this lie 

 layers of thin-walled, long cells, the bast 

 layer, through which run the laticiferous 

 vessels, which are of some length and 

 which branch and join each other at intervals so 

 as to form a network. Below this layer lies the 

 cambium or growing layer of the bark, and below 

 this again the wood. The latex vessels are most 

 abundant near the cambium layer, and run verti- 

 cally, parallel with the long axis of the stem. 



To get the latex it is necessary to cut the bark 

 in such a way as to cross as many latex-tubes as 

 possible without unduly injuring the tree. A notion 

 holds that the wound should not penetrate the deli- 

 cate cambium layer but stop short of it for fear 

 of risking the life of the tree. As a matter of fact, 

 in Para rubber, at least, the risk is small. Many 

 trees have been cut to the cambium and deeper in 

 the Singapore Botanic Gardens, but none have been 

 injured ; reports from Ceylon, however, recommend 

 great care in this respect. Less deep wounds heal 

 more quickly, it is true, but as the greater part of 

 the latex vessels lie very close to the cambium, 

 unless the wound is made to this layer not more 

 than half the available latex can be secured. 



