70 THE WHOLE ART OF RUBBER-GROWIXG 



Many of them showed a clean straight bole of 20 feet, 

 which is typical of the well-grown Manihot, whilst 

 others had branched at 4 feet from the ground, and 

 were dwarfed and bent in consequence. Seventy per 

 cent, of the whole were found suitable for tapping. 

 The kind of knives used for tapping Hevea in 

 Ceylon were found to be useless at Hawaii owing 

 to the fine texture of the outer bark of the Manihot, 

 and a special form of cutter had to be devised. After 

 many experiments the half-herring-bone system was 

 adopted, the full herring-bone being found to result 

 in the partial strangulation of all the milk-yielding 

 vessels situated between the upper and lower laterals. 

 The half-herring-bone system, as is well known, 

 consists of one vertical cut, with the laterals 

 12 inches apart halfway round the tree. As in the 

 case of all true Manihots, the latex was found to 

 coagulate very quickly — almost immediately — on the 

 opening of the laterals. To prevent this a system of 

 water-dripping over the cut surface was tried with 

 some success, but it was found that by the addition 

 of a small proportion of ammonia to the water 

 coagulation was entirely suspended for several days. 

 Tapping was always done either in the early morn- 

 ing or late in the evening, and in a general way it 

 was found that the flow of the latex was more certain, 

 more uniform, and greater in output at the evening 

 tappings. 



Manihot is propagated either by seeds or 

 cuttings. In East Africa the latter method is 

 preferred. The cuttings are taken from the best- 

 grown trees. They should not exceed seven-eighths 



