Some Experiments on the Action of Wood 
on Photographic Plates. 
BY 
HELEN STUART WILLIAMSON, 
Imperial College of Science and Technology , London. 
With Plate XI. 
D R. RUSSELL 1 discovered that certain woods have a definite action in 
darkness on a photographic plate. The present investigation was 
undertaken in order to ascertain whether this action provides a suitable 
method, first, for determining the incidence of decay before it is macro- 
scopically visible ; second, for observing the effect of exposing wood to 
various temperatures and degrees of moisture and its bearing upon the 
means of recognizing wood that has been kiln-dried ; third, for the identifi- 
cation of timbers. 
The interesting behaviour of the Pines in this connexion has been 
pointed out by Russell. He found in Scotch Pine, for example, that the light 
rings, i.e. the spring wood, have acted on the plate, giving dark rings, and 
that the autumn wood is without any action. All the Pines he investigated 
agreed with this, whilst the Larch gave a reverse picture, having the spring 
wood inactive and the autumn wood active. Professor Brereton Baker has 
proved that this action on the photographic plate is due to hydrogen per- 
oxide given off from the wood. Experiments made during the course of 
this investigation show that there is no question of enzyme action, since 
steaming at ioo° C. does not permanently destroy the activity of the 
wood. 
In some woods, such as bass (lime) wood, Dr. Russell points out, 
a picture is formed which is not visible to the naked eye nor when a lens is 
used. It seemed possible, therefore, that this method might be a means of 
identification of timber and also might reveal the first sign of decay, making 
it easy to adopt remedial measures at an early stage. 
Method. 
The method employed was to place a specimen of wood on a photo- 
graphic plate in the dark, usually with the smooth planed transverse surface 
[Annals of Botany, Vol. XXXVI. No. CXLI. January, 1922 1 
