In previous experiments it was found impossible to duplicate results of Hoyem and Tyndall who found a ``range'' for the successful growth of single crystals of zinc. Most specimens were ``optically mosaic.'' It is now shown that by adding Cd to Zn of highest purity, single crystals may be grown and that a ``range'' is connected with their growth. The range is similar to, but not identical with, that of Hoyem and Tyndall. Moreover, the shape of the range is dependent on the Cd content and on the speed of growth of the crystals. Optical mosaics as well as the changes of Hoyem and Tyndall are found outside of the range. In general optical mosaics are less frequent the higher the Cd content. Certain surface markings appear on the crystals even for only 0.20 percent Cd. These are believed to be identical with markings previously described by Rosbaud and Schmid and by Straumanis and probably indicate concentration of Cd along basal planes.