448 THE POPULAR SCIENCE MONTHLY 



different knives have been invented for the purpose. The half-herring 

 bone method is considered the better as being less severe on the tree. 



A very curious phenomenon was observed in the early experiments 

 on tapping. It was found that if a second incision was made in the bark 

 of Hevea, near one cut a couple of days previously, there was a greater 

 flow of latex than if the second incision were made at a distance, say, on 

 the other side of the tree. More than that, the latex flowed more freely 

 than on the first incision. In a particular experiment on four trees, 

 tappings were made at intervals of five days, and the volume of latex 

 increased from 61 c.c. at the first tapping to 449 c.c. at the fourteenth, 

 when the series was ended. In view of the fact that the latex from later 

 tappings is thinner than that from the first, another series of experiments 

 was made on ten trees which were tapped every day for a fortnight and 

 the rubber content of each tapping determined. This rose from 64/ oz. 

 on the first day to 33f oz. on the fourteenth. Within limits a thin latex 

 is the most satisfactory, the latex from the first incision often being of 

 little use because it coagulates before reaching the proper receptacle and 

 so gets mixed with the bark of the tree and other foreign .matter. Some- 

 times drip pans are fastened to the tree above the incisions, and water 

 dropping upon tire incisions prevents the latex drying on the tree. 



The peculiar action of Hevea owing to which subsequent tappings 

 near the previous incisions produce a greater flow of latex is called 

 " wound response/' and no other rubber-bearing plants show wound re- 

 sponse in anything like the degree shown by Hevea; in fact, it may be 

 doubted whether the phenomenon occurs in the other genera at all. As 

 compared with Hevea, Castilloa gives a greater flow of latex on the first 

 incision, some five or six times as much. But if, after a couple of days, 

 a further incision is made near the former one, little or no latex flows 

 from it, while, as we have seen, there is in the case of Hevea a greater 

 supply than before, roughly about twice as much, which persists through 

 subsequent tappings. Accordingly, in tapping trees a very thin paring 

 (about one twentieth of an inch) is removed each day or each alternate 

 day. As the first incisions are made about a foot apart, it takes some 

 two hundred and forty parings before the bark is all removed from this 

 part of the tree, and as by the half-herring-bone system only about a 

 quarter of the tree is tapped it takes about four years to remove all the 

 bark and by that time operations can be begun again on the new bark 

 that has formed in the meantime. 



The arrangement of laticiferous vessels in Castilloa is different from 

 that in Hevea; in the former the vessels all connect in a somewhat simi- 

 lar manner to that of veins and arteries in the body. Hence, when the 

 vessels are cut, there is likely to be a drain from a large area. In Hevea 

 the tubes arise from a breaking down of cell walls which occur from 

 time to time and so the latex does not flow out so freelv at first. Possi- 



