May 



1906.] 



THE INDIA RUBBER W^ORLD 



255 



NOTES ON THE "CASTILLOA" RUBBER TREE— 11. 



WHAT latex is to the tree is still a debatable ques- 

 tion. I think that it is simply a protection 

 against insects and evaporation whenever the 

 tree is wounded. Anything striking against the 

 outside bark, if it hits hard enough, will bruise the inner 

 bark so that the latex flows. An examination of this place 

 a day or two later will show a thin coat of rubber entirely 

 covering the bruise. Tropical trees do not have the thick 

 outer corky bark of northern trees. Anything striking 

 them is liable to bruise the inner bark. This sheet of rubber 

 forming would protect the bruise from too much evaporation 

 and from insect attacks. Leaf cutter ants do not attack the 

 leaves of Castilloa and cattle do not seem to be fond of them, 

 but I believe that this is not due to the latex but due to the 

 thick coat of epidermal hairs, a thing which few tropical 

 trees seem to possess. It is noticeable that ants do attack 

 Hevea, which has not a hairy leaf. 



The study of the structure of the latex shows tliat it has 

 two distinct parts — waterj- solutions and solid substance in 

 minute globules. The watery solutions contain no rubber. 

 They do contain the substance which forms the residue of 

 the black water, though this substance is apparently changed 

 by oxidation before becoming black water. They may also 

 contain sugars and proteids, as these substances are evident- 

 ly there, but it is more than likely that these substances are 

 not in the original latex but come from some other bark tis- 

 sue than the " milk tubes." 



The solid globules are principally rubber but thej' are said 

 to be surrounded b}- protoplasm and contain a nucleus. In 

 that case they would be cellular in their nature. As the 

 tube in which they are enclosed is already' a cell, it would be 

 a case of a cell within a cell, which is rather rare in botany. 

 At the same time they are very small for cells. I have not 

 been able to examine the structure of the single globule, as 

 my microscope is not powerful enough, but I think that they 

 are not cellular but are originally chromotophores in which 

 rubber has been stored. In that case they would be formed 

 in a similar manner to starch grains in a potato and other 

 roots. I believe that this is the case and that the substance 

 in solution, later forming the black water, bears the same 

 relation to rubber that sugar does to starch ; that is, they 

 are similar forms of carbohydrates which can be readily 

 changed from one to the other by the action of an enzyme, 

 and when they are to be transported from the soluble sub- 

 stance and, when stored, the solid substance. This state of 

 things seems to be the same in all latex bearing plants, as 

 all that I have examined contain this watery solution and 

 the solid globules, though the waterj' solution doesn't al- 

 ways turn black and the solid globule is not always rubber, 

 but sometimes a sticky substance. 



Dr. Weber asserted that the black water was due to oxyda- 

 tion and he believed that rubber itself was an oxydation 

 product. Latex which is gathered and quicklj- corked up 

 away from the air, forms no black water. Black water gets 

 blacker for longer standing in the air until about five da^'s 

 after gathering. Fresh black water can immediatelj- be 

 turned to its deepest black bj- ammonia, but ammonia will 

 not affect black water five days old. I believe that the ac- 



tion of ammonia is the same as the oxj'dation in the air. 

 Contact with metals will make black water blacker. Sugar 

 slowly takes the black color away and latex which has not 

 been allowed to oxydize has water which resembles that 

 formed by sugar. I believe that sugar reduces it to its form- 

 er state. I do not see any reason to think that rubber itself 

 is an oxydation product. It is possible, but if so it can be 

 further oxydized by the use of nitric acid. 



The problem of tapping has a great deal to do with how 

 the latex is situated in the tree. According to most writers 

 it is carried in "milk tubes " which are in the bark and 

 are arranged vertically. I have not found anj' writers who 

 seem to know what these milk tubes are like — whether the 

 latex runs up or down in them, or what connection these 

 milk tubes have with other parts of the plant. When I first 

 got here I tried a number of experiments, trying to increase 

 the flow of latex by multiple tapping, gradual tapping, and 

 so on, but all these failed. The reason for these failures I 

 now attribute to the shape and position of the latex carrying 

 tissue in the plant. This tissue, I believe, is the part known 

 as the bast fiber. Bast fibers are long fibrous threads, taper- 

 ing to a point on each end, having a thick, tough wall and 

 in most plants dead, and containing nothing in the cell 

 cavit}'. 



In the Castilloa, the microscope shows that the bast fibers 

 have a larger cell cavity than in most plants. It is reason- 

 able to suppose that they are in such cases alive and contain 

 something. I have seen no other tissues in the Castilloa 

 bark which contain the latex and therefore believe that these 

 bast fibers do. The bast fibers are arranged vertically and 

 are probablj' only a few inches long. Those I have exam- 

 ined in temporary' branches were from i to 3 inches, but they 

 are probabU- longer in older parts of the trees. The fibers 

 are probably connected to each other by pits but I have not 

 been able to locate these connections. These pits would not 

 allow solid substances to pass from one fiber to another, but 

 would allow water and water}' solutions. 



The rubber being in solid globules is probabl}- formed 

 right in the fiber itself. The fibers are not arranged in regu- 

 lar joints, as was the opinion of Carlos Berger, but are irreg- 

 ularly arranged, the tapering end of one fiber fitting between 

 other fibers. When the fibers are cut across by a tapping 

 instrument their content is ejected by bark pressure. Such 

 a cut will take latex from the tree only for a distance of 3 or 

 \ inches each side of the cut. This shows that the latex does 

 not run up and down the tree or from one fiber to another 

 If no more cuts are made, the latex will not be renewed in 

 the cut fiber for some time (not entirely for about 3 months), 

 although the surrounding fibers are full of latex. This shows 

 that all the latex from the tree cannot be taken from one cut. 



The distance apart that cuts should be made around the 

 tree is a disputed subject, and depends not only on the length 

 of the bast fibers and the way to get the most yield, but also 

 on the amount of injury done to the tree. If yield were the 

 only consideration, one foot would be a good distance and 

 would give, I believe, the maximum yield. Eighteen inches 

 will give close to the maximum, giving enough more latex 

 from^each cut to make up for the fewer cuts. Both of these 



