It has been shown in former papers that if wood, even if old and dry, be placed on a photographic plate in the dark, it is able to act on it in such a way that when the plate is treated with an ordinary developing solution a clear picture of the structure of the wood is produced. Further experiments on this and allied subjects have been made, and interesting results obtained. After experimenting with a large number of woods the conclusion is that, almost without exception, they have this property of acting on a photographic plate in the dark. The amount of action exerted, however, varies very considerably with different woods, some requiring a much longer time to produce a good picture than others. The ordinary limits of time and temperature are from ½─18 hours’ exposure and from ordinary temperature to about 55° C. The time of exposure may be extended to 30 or 48 hours, but a higher temperature cannot be used, since plates, as a rule, are damaged when heated above 55° C. This action occurs both when the wood is placed in contact with the plate and when it is supported above the plate.