It has already been ascertained that crystallization of rubber can be induced in various ways, such as stretching, freezing, milling and compressing. if a narrow strip of smoked sheet rubber is stretched extensively, the x-ray diffraction pattern shows a fibrous arrangement of the microcrystals. At an elongation of about 150 per cent, a faint fibre diagram is obtained and at 500 per cent elongation, the diffraction spots become sharp and intense. The amorphous halo peculiar to unstretched rubber remains unchanged in width and position, but its intensity decreases with increase in elongation, in contrast to the increase in intensity of the fibrous spots. It was found by Katz and Bing that crepe rubber is crystalline. This point was confirmed by Tanaka and the writer; the Debye-Scherrer rings obtained by them with crepe rubber is shown in Fig. 1 of Plate I. In preparing a sheet of crepe rubber, coagulated strips are passed between rolls 8 to 12 times, and the coagulated strips are strongly crystalized by such severe milling. In preparing smoked sheet, milling of the coagulated sheets is not so severe as in the case of crepe rubber, and some of the rubber crystals formed during milling melt when heated in the process of smoking.