Mah. 1897.] BOTANICAL SOCIETY OF EDINBURGH 45 



museum preparation, already polished or ground, as the 

 case may be, and get a representation of its structure 

 showing detail enough for purposes of identification and 

 comparison, without in any way damaging the preparation. 



PREPARATION OF THE SPECIMENS. 



No sectioning is required, as only the specially-dressed 

 opaque surface of the block of wood is micrographed. If 

 one have the blocks of wood at one's disposal, the first 

 thing is to get the transverse or longitudinal surface which 

 it is desired to photograph as smooth and clean cut as 

 possible. Tliis is accomplished by aid of a heavy steel 

 dressing-plane, the finishing strokes with the plane being 

 all in the same direction. Avoid sandpapering the 

 surfaces. In the case of specimens which have unfortu- 

 nately been sandpapered, a new series of artificial characters, 

 consisting of very fine strias is introduced, and a photograph 

 of such a surface presents a general " fuzziness " which 

 very unpleasantly masks the diagnostic points. This may 

 be remedied to a certain extent by rubbing the surface of 

 the block with a wet sponge immediately before the photo- 

 graph is taken. 



In the case of museum specimens, which are polished 

 or varnished, satisfactory results may be obtained by 

 lengthening the time of exposure, varying the intensity of 

 the light, and also the angle at which the incident rays 

 from the radiant strike the surface. The varnished or 

 polished surface acts to a certain extent as a mirror, and 

 introduces some difficulties. The same difficulties are 

 encountered in dealing with polished surfaces of silicified 

 wood, but these troubles are overcome in the way above 

 described. In well ground and polished fossil specimens, 

 one obtains, with a little care, very sharp negatives, 

 showing almost as much minute structural detail as in an 

 actual micro-section — a result which cannot be looked for 

 in the case of recent woods, unless they are very hard and 

 highly polished. 



The best results are got in the latter case, when the 

 photograph is taken of the surface immediately after being 

 dressed, before the pores have had time to fill with dust, or 

 before any discoloration has set in. 



