Prior to initiating these studies, the callus was transferred to fresh medium and
grown in the dark for several months. The dark-grown callus was opalescent,
having lost all traces of pigmentation, relatively homogeneous, and the tissue masses
had become smaller and more friable. The tissue was subcultured routinely at
monthly intervals and displayed a fivefold increase in fresh weight during successive
transfers. Portions of this tissue, approximately 100 mg fresh weight,
were used to inoculate no less than 12 tubes for each set of experimental media.