RUBBER 445 



Another interesting source of rubber is the genus Landolpliia, of which 

 there are several species noteworthy as being creepers. This genus pro- 

 vides most of the Congo rubber and belongs to the order Apocynaceae. 

 Ficus elastica spoken of above is one of the genera of the order Urti- 

 caceae of which another genus is Castilloa also already mentioned as 

 found in Mexico and one of the very first plants to attract attention as 

 a rubber producer. 



Rubber, though found to a slight extent as a solid deposit in the 

 woody fiber of certain species, is almost entirely obtained from the latex 

 of the rubber-bearing plants. The latex is a fluid usually more or less 

 viscous which is carried in vessels, the laticiferous vessels, lying in the 

 inner bark just a little outside of the cells which carry the sap. The 

 caoutchouc itself is in globules of microscopic or sub-microscopic size, 

 being from 1/50,000 inch to 1/6,000 inch in diameter, and forms an 

 emulsion with the suspending liquid. A familiar example of latex is the 

 exudation of the milkweed. The function of latex in the plant itself is 

 unknown. ' It may be an excretion, it may be intended for the preserva- 

 tion of the tree from attack by fungus or insects or other enemy. The 

 process of raw rubber manufacture consists in the collection of the 

 latex and the coagulation from the serum of the emulsified particles. In 

 tapping the trees the essential thing is to cut deep enough into the bark 

 to sever the laticiferous vessels, but not to cut into the cambium, the 

 living layer of cells from which both the wood and the bark of the tree 

 are produced. In the Amazon Valley this is usually done by a small axe, 

 the incisions being of a V shape, the first being made at a height of about 

 six or seven feet. Later incisions are made at intervals of about two 

 inches below the previous ones, till the base of the tree is reached. Then 

 tappings are begun on the other side of the tree in the same order as 

 before. The latex is collected in a small cup fixed to the tree by moist 

 clay and is removed from time to time. Five pounds of latex is con- 

 sidered a large amount from one tree during the season. The latex is 

 gathered from the cups into a pail and is cured by the smoke of a fire 

 rich in tarry and acid matter. A long wooden rod has rubber latex 

 poured over it and the thin layer which sticks to the rod is dried in the 

 smoke. Over the sheet thus formed is poured more latex, which is also 

 dried in the smoke. Thus layer after layer is produced till a ball weigh- 

 ing from twenty to one hundred pounds is obtained. Thus is made raw- 

 fine Para rubber. Some of the latex coagulates on the tree, forming a 

 scrap rubber which is collected and compressed into irregular masses 

 called " negroheads." 



It is not my purpose to describe all the processes through which raw 

 rubber passes before it appears in the shape of golf balls or automobile 

 tires or in any of the many forms in which it comes into commerce, but 

 a very brief outline may be given. First, the raw rubber is cut into 



