Gums, Resins, 



18 



too shallow. Between the bark and the wood is the growing part of the tree known 

 as cambium. This part alone has the power of forming new bast and new wood. 

 If a cut is made which does not go into the cambium, the cut will not heal 

 over with new material. Of course it will dry up and turn black, and in this way- 

 protect the tissue under it, but the piece of bark taken out is gone for ever. On the 

 other hand a cut made just to the cambium will heal quickly. The first signs of 

 healing appear between one and two weeks after the cut is made, and in two months 

 at the latest the cut is Avell healed. In time the whole cut will fill with new 

 material which contains latex, and can be tapped again if necessary. 



Another strong reason why the tool should cut to the cambium is that not 

 only does the shallow cut miss cutting some "milk tubes," but it misses a very 

 large proportion of the "milk tubes." The " milk tubes " are formed by the 

 cambium in layers. The ones closest to the outside bark were formed when the 

 tree was very young, and small in circumference, say eighteen or twenty inches. 

 The spaces between these tubes are filled by medullary rays which run from the 

 pith outward through the wood to the outside bark. Therefore the outermost 

 layers contain very few milk tubes, the next more, etc., until the innermost layer 

 has the most, since it was formed when the circumference Avas greatest. This is 

 borne out by facts. A much larger yield is actually obtained by cutting into the 

 cambium than by cutting almost into it. 



Another thing to be avoided is cutting too deeply. When a cut goes through 

 the cambium into the wood, the healing commences at the edges of the cut cambium 

 and has to spread slowly, making new cambium before it can make new bark or 

 wood. If too much wood is exposed in this case it will often dry up before the 

 cambium can heal over, and in that case it never heals. I have seen an old machete 

 cut with half-an-inch of wood exposed, the bark thoroughly healed all around it. 

 I was told that it had been that way without healing for two years. 



The shape of the groove cut in the tree is a case for investigation. Whether 

 the V-shape should be wide or narrow is under dispute. Those who do not believe 

 in taking away bark would argue that it should be as narrow as possible, and 

 yet hold the milk. At least one planter here thinks that the wider cuts yield 

 better. I see no reason why they should except that possibly the flow would 

 be checked in a narrower cut by its becoming blocked with rubber. I am 

 inclined to think that the narrower the cut the better, and that it might be 

 possible to have such a tool that the groove would be cut entirely in the outer 

 half of the bark, the inner tubes being cut by a single blade cutting to the 

 cambium. Such a blade could hardly cut the wood, but could cut all milk 

 tubes. A pocket knife cut heals more quickly than any other, but of course makes 

 no groove for the milk to flow in. 



WHEN TO TAP. 



The time to tap is another point. There appears to be no reason why 

 the trees should not be tapped at any time during the rainy season. I should 

 imagine that the driest season, in March and April, would be a poor time, but 

 I have not been here during that season. Rain generally makes the milk rather 

 watery, and makes it flow more freely, but I have never seen it so watery that 

 it would not pay to tap, except in a tree which had been recently tapped. 

 Tapping in heavy rain would not do, as it would wash the latex, which does 

 not flow into the cups, and might fill up the cups and spill the latex in them. 



Temperature affects the flow of latex very noticeably. The yield of rubber 

 is much greater in the early morning than at any other time of the day, and 

 always decreases towards noon and increases towards night. This is not so notice- 

 able on cool cloudy days. It would probably not be so noticeable in a shady 



