IN a previous paper1, a method has been described for the detection of the enzyme phosphorylase in plant tissues. Briefly, it consists of incubating freehand sections of the tissue, previously freed of starch by starvation, in a buffered solution of glucose-1-phosphate, and subsequent staining in iodine–potassium iodide for the resultant starch. With this method a survey has been made of the distribution of phosphorylase in the tissues of many higher1,2 and lower3 plants. An interesting outcome of these observations is the finding that the enzyme is localized, solely in the plastids. The evidence may be summarized as follows.