ON THE NATURE OF TRUNK BARK PRODUCTION BY YOUNG CINCHONAE

Resumen

Variations in trunk circumference and in bark dry weight per unit area of trunk surface in three species and a hybrid of Cinchona
have been studied as functions of vertical position on trunk. The trees were between three and four-and-two-tenths years of age from transplanting.
Circumference in the trees examined varied according to the type equation Y = a + b X - c X² except in the case of undersize trees of the same age in which case the relationship was Y = a + b X. In both cases Y is circumference and X is distance from terminal bud,
while a, b and c are constants for an individual tree.
In the main, bark dry weight per unit area of trunk surface varied with downward position on trunk according to three different type equations depending upon the specíes concerned. In each case Y is bark dry weight per unit area and X is distance from terminal bud on trunk: a and b are constants for a single tree. Cinchona Calisaya and also apparently C. Ledgeriana followed the type equation Y = a + b long X. C. succirubra obeyed the type equation log Y = a + b X, while the Hybrid between C. Ledgeriana and C. succirubra followed all three relationships but tended in the mean of six cases to follow the type Y = a + b X.
Assuming equal or nearly equal growth rates and trunk dimensions in all four cases, it is concluded that the species examined
herein may be ranked according to their inherent bark producing capacities as follows:
Calisaya and Ledgeriana > Ledgeriana x succirubra > succirubra. With the exception of the extremely slow-growing Ledgeriana clone utilized in the present study, actual bark yields, allowing for age differences, conformed to this rating. Whether such relationships extend to commercial maturity and whether the interspecific differences indicated herein are real must be determined by further study involving much large numbers of trees.
The present study, therefore, identifies two new variables in Cinchona bark production that bear upon the problem of selecting
high-yielding mother trees for clonal propagation. These variables are (1) the shape of the trunk (e.g ., whether conical or barrel-shaped) and (2) the relative dry weight of bark per unit surface area of trunk and the rate at which this function decreases from base toward tip of trunk.