44 TRANSACTIONS AND PROCEEDINGS OF THE [Sess. lxt. 



On THE Photomicrography of Opaque Stem Sections — 



PiECENT AND FOSSIL. By Pv. A. PtOBERTSON, M.A., B.Sc. 

 (Read 11th March 1897.) . 



Everyone engaged in research work or teaching has felt 

 the great need of a method of reproducing accurately the 

 diagnostic characters of timber as seen in transverse and 

 longitudinal section. Drawing each surface by hand, in 

 detail, is a slow process, even although such gave satis- 

 factory results, whicli it does not, the personal equation of 

 the artist always making itself felt. An ordinary razor- 

 cut section is rather small, and does not present surface 

 enough to exhibit, typically, all the characteristic appear- 

 ances. Presides, the characters important for purposes of 

 identification are apt to be lost sight of in the multitude of 

 details presented, when such a section is micrographed. A 

 large area is a necessity, as the character of the wood is not 

 constant, but changes with age. There is the method of 

 preparing large sections by means of the hand-plane.* This 

 method, w^hile giving excellent results irro tanto, is objection- 

 able for this special purpose, because of the difficulty of 

 getting such sections exactly transverse, of the tendency of 

 the cell membranes to become torn, and of the time required 

 in preparation of tlie block, even before sectioning can be 

 begun, not to speak of the labour, patience, and time 

 necessary to secure even one satisfactory preparation. 

 Again, in dealing with rare or museum specimens, one 

 cannot always get carte Uanche to cut and carve the 

 preparations for the purpose of sectioning as described. 



The objections to these methods are still stronger when 

 one is dealing with fossilised stems. The cutting of 

 sections in this case, and the subsequent grinding necessary 

 to obtain a preparation thin enough to be transparent, is a 

 tedious process, requiring considerable manipulative skill, 

 and the oljjections to cutting up museum sjjecimens in this 

 case are very pronounced. To overcome these difficulties, 

 is the aim of the method which follows : to take the 



* A magnificent eeries of hand-plane sections of British woods was 

 exhibited to this Society some years ago by Professor liayley Balfour. 

 'J'his scries is in the Kesearch Laboratory at "tiie Jloyal Botanic Garden. 



