Mau. 1897.] BOTANICAL SOCIETY OF EDINBUKGH. 49 



the dark slide and plate are inserted in place of the screen, 

 the ribbon lighted and slowly fed throngh the tube, the 

 shutter drawn, and the plate exposed. Some surfaces 

 require longer than others, but an average exposure of forty 

 seconds was sufficient. 



In developing the plates, I use a pyro-soda fluid. It 

 gives a thinner but also cleaner plate than pyro-ammonia — 

 two characters which are not undesirable in this instance. 



Should a plate, on development, be found to be over or 

 under-exposed, I prefer to make a fresh exposure, utilising 

 the experience gained from the first failure, rather than 

 waste time " doctoring " the plate, which seldom gives 

 satisfactory results. 



Good effects are got with bromide prints, gelatino 

 chloride, and also with sodiotype, which last approaches 

 in colour in some cases the natural tint of the wood. 



As a speedy and reliable method of obtaining accurate 

 representation of the diagnostic characters of timber for 

 museum and teaching purposes, for comparative and 

 research work, and also for identification of timber, I 

 find the above all that can be desired. It is specially 

 valuable for teaching purposes, as only the important 

 diagnostic details are brought out to the exclusion of the 

 minor though not less interesting structural characters. 



SECOND METHOD. 



Photomicrographs of smaller areas of surface under a 

 somewhat higher magnifying power are useful in the com- 

 parison and elucidation of points of detail, e.g. the sinuous 

 tangential lines of vasa in the autumn wood of Ulmus, and 

 the similar lines of parenchyma in corresponding positions 

 in the oak and certain fossil woods, etc. 



Such may be obtained by using the microscope with a 

 low-power objective of one, two, or three-inch focus in place 

 of the photographic lens of the first method. In this con- 

 nection, it is necessary to use a microscope in which the 

 stage and all the usual substage mechanism is removable, so 

 as to allow of the block of wood being brought within focus 

 of the lens. Further, I have found it useful to have a 

 small apparatus with an iris-diaphragm to screw on to the 

 end of the microscope tube behind the objective. Leitz 



TUANS. HOT. SOC. EOIN. VOL. XXI. E 



