The bark is thickest near the base of the tree, and it is here that the greatest flow of latex is obtained. On 29 trees tapping was carried on by six V cuts placed each one foot below the next, the lowest cut being one foot above ground level. Continuous paring for nearly six months produced the following yields of latex from the different cuts.
Height above ground level, feet
Yield of latex, cubic centimetres
The lowest cut of all gives a very much larger yield than any of the others, owing to the fact that it drains a larger area of bark, and one which is in free communication with the covering of the roots. The five upper cuts are more nearly comparable with one another. These show a steady slight increase in yield in passing down the stem. The latex from the lower cuts also contained a slightly higher percentage of rubber than that from the upper cuts.
Incidentally these figures afford further evidence in support of the conclusion that the bulk of the latex obtained is manufactured locally. If the latex passed down in large quantities from the upper part of the trunk and then flowed laterally into the tapping area, we should expect a larger flow from the topmost cut than from the cuts immediately below it. As a matter of fact the reverse is the case.
The yield of latex at six feet from the ground was rather more than three-fifths of the yield at two feet in the case of this particular experiment. The only reason for confining tapping to the lowest six feet of the trunk is therefore one of convenience. Profitable yields could doubtless be obtained at a considerably greater altitude, but this would entail great loss of time in tapping, owing to the necessity of climbing the tree.