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Hugo P. Kortschak, a shy, quiet Quaker with unbelievable generosity toward mankind; an accomplished musician; and a dedicated, tenacious, and brilliant scientist, who spent his entire professional career working for a single employer in a commercially-oriented research organization, made one of the outstanding contributions to biological science of the past century. With his colleagues in the Hawaiian sugar industry, he discovered the C4 pathway of photosynthesis.

Sugarcane tissues subcultured for over 4 years had lost the capability to differentiate shoots. In freshly isolated tissues from 3 cultivars, we readily obtained shoot differentiation on Murashige-Skoog medium, but shoot differentiation was lost, apparently irreversibly, after more than one subculture on a modified White's medium. Tissue from a fourth cultivar produced only roots. The tissue cultures of all cultivars studied have the capability to form roots regardless of the length of time in culture; root formation was enhanced by treatment with dalapon (2,2-dichloropropionic acid).

Evidence is presented for the increased excretion of amylolytic enzymes into a sugarcane cell culture medium when starch was substituted for sucrose as an energy source. The excretion was further enhanced by the inclusion of 1 mum gibberellic acid in the nutrient medium. The growth rate of the cells increased after they became adapted to starch relative to cells grown on sucrose, but the rate of amylolytic enzyme excretion remained unaltered. Amylolytic enzymes in the medium included alpha-amylase but the identity of one or more other enzymes related to starch hydrolysis remains in doubt.

The growth rate of plant tissue cultures is substantially increased through the use of a large-volume carboy system. Aeration is considered to be the most important factor. With this system, yields of a pound or more of tissue can be obtained within 2 weeks.