The production of xylem and phloem elements by the cambium of Eucalyptus camaldudensis was investigated. Plants grown under various climatic treatments were exposed to 14CO2 for short periods. This treatment left a marker in the xylem and in the phloem cells derived from the cambium during the exposure. Thus, the newly formed cell layers could be counted. Results reveal that the ratio of the number of xylem layers produced to the number of phloem layers produced (4: 1) is practically independent of many environmental factors. The ratio was also found to he independent of the rate of cell production as well as of the width of the undifferentiated cambial zone.

Changes in the ratio of xylem to phloem were not found in plants treated with naphthalene acetic acid, kinetin or triiodobenzoic acid, nor in plants which were defoliated or disbudded. However, a higher ratio was found for plants treated with gibberellic acid.