.Tax. 1899.] BOTANICAL SOCIETY OF EDINBURGH 165 



slide is placed in contact with these, and clamped down 

 very firmly, so as to ensure the expulsion of all air-bells 

 and to have the surfaces uniformly in contact. The plate 

 was exposed to the light of an ordinary gas-burner ; the 

 time of exposure was varied, so as to ascertain what gave 

 best results — a long exposure to a weak light, or a short 

 exposure to a strong light. After exposing, the plate was 

 washed — in the case of clove-oil preparations, in alcohol, 

 followed by water; in the case of glycerine preparations, 

 in water merely. The plates, which were Ilford, were 

 developed with hydroquinone, and experiments showed 

 that, if anything, better results in the way of finer detail 

 were got with a weak or used developer than with a 

 developer of full strength. The interesting researches of 

 Forgan, in " Proc. Brit. Astron. Assoc," and Carlier, in 

 " Proc. of Scot. Mic. Soc," 1896—97, were very suggestive 

 in this connection. 



The general results varied — the variation depending on 

 the ordinary factors, as exposure and developer, and on the 

 additional ones of thinness and staining. The necessity of 

 cutting sections of large size from the material described, 

 prevented the minimum of thinness being obtained, and 

 therefore precluded the best results being made of the 

 method. 



In other work, where serial sections smaller in area, and 

 therefore capable of being cut thinner, serve the purpose, 

 much better results are possible. As it is, the advantages 

 may be summarised as follows : — Serial sections can be 

 obtained on one slide, — being contact preparations, they are 

 all of the natural size ; the plate can be used as a lantern 

 slide directly, or as a negative to give paper prints, — for 

 comparative work, such as described above, it gives enough 

 detail; it stands examination and projection under an ordinary 

 two-inch objective, the thickest sections giving at least the 

 medullary rays, annual rings, pores of the wood, and 

 part of the intervening tissues, the thinner ones showing 

 the intermediate tissue more or less distinctly, and capable 

 of standing examination, in some cases, with a one-inch 

 objective. Beyond this magnification, the difficulty becomes 

 technical, and concerns the emulsion itself and the grain of 

 the plate. 



