ABSTRACT
Histological, histochemical, and cytological research on significant differences between abnormal bark and producing bark have brought some replies to the question and a more precise definition of bark dryness. Browning of dry bark was mentioned very early on; authors in the 1920s reported abnormal coloration: the bark, whose natural color varies from yellowish to brown-yellow, acquires a darker brown to gray color in places. Drops of latex do not appear whatever the depth of the tapping cut; this drying through the whole depth is a feature of bark said to be dry to the cambium. Flaking generally begins at the tapping cut, but may also be separate from it. Other anomalies are observed in dry zones in bark: browning, a tendency to thicken, cracking and peeling, deformation, and abnormal trunk vigor. Bark dryness in Hevea brasiliensis is a complex phenomenon which involves a varied set of mechanisms and which probably has various causes.
