1. A reagent (p-cresol) has been used to determine the activity of tyrosinase in the potato tuber.
2. The course of the reaction tyrosinase-p-cresol has been shown to be mono-molecular, with a short linear period at the commencement. From observations of this period, constants for the enzyme activities have been obtained and a temperature coefficient deduced.
3. The enzyme activity has been shown to depend upon stage of maturity of tuber, variety of tuber, and disease infection, but to be independent of tuber weight, environment, season, and storage conditions.
4. The probable significance of the results has been discussed.
The writer wishes to thank the Department of Agriculture for Scotland for a Grant which enabled the work to be carried out, and also Dr A. Lauder and Dr A. M. Smith of the Edinburgh and East of Scotland College of Agriculture for their interest and assistance throughout the course of the work.