Washed aerated disks of mature tubers of H. tuberosus developed invertase and ascorbate-oxidase activities; this effect was not due to contaminating micro-organisms. 2. The use of specific inhibitors showed that such development was an expression of protein synthesis. 3. There was no visual evidence of cell division during induction of the enzymes. 4. The invertase could not be solubilized; most of the ascorbate oxidase was freely soluble.