You may wonder how it is possible to choose the right tree to be removed in doubtful cases. This is where the combined field and laboratory work comes into play, which has indeed made the cultivation of Cinchona plants great. It has made it possible to make precise field decisions based on laboratory research. A selection method, found and perfected at the Government's Cinchona Plantation in Tjinjiroean (meaning the bee river; Tjai (river) becomes Tji and Njoeran is bee), is currently being applied as follows.

Starting from the grafting point of the trees, a line is drawn at a meter height with paint that contrasts sharply against the brownish-green bark (orange). The circumference of the tree is measured at regular intervals, usually twice a year.

Just above this line, a round disc of bark is extracted from the tree using a precisely calibrated hollow punch, sharpened at the front. The inside diameter of this hollow punch is exactly 1 square cm. This piece of bark is dried and analyzed, after which the amount of quinine in a 10 cm cylinder is calculated. This is the comparative figure between the various trees, which accurately indicates the merits of the different trees.

Based on these figures, the value of each tree can be determined. I will come back to this later. And then, after four to five years, the once reduced but now more valuable plantations of young, practically non-producing complexes will have become productive Cinchona gardens. Regular thinning and pruning yield the Cinchona bark, which is harvested in the manner to be described.