PALEOBOTANY 721 



away with hydrofluoric acid. The preparation, after washing, 

 can be ke})t dry and examined by reflected hght, or mounted 

 in glycerin jefly under a covershp. It cannot be mounted in 

 balsam. The method makes possible an examination of both 

 surfaces of carbonised plants. It is a development of the collodion 

 film method of Nathorst (Geol. Foren Forhondl., xxix, 1907 ; see 

 also Bather, Geol. Mag., Dec. v, iv, 1907). 



Ashby's Cellulose-Film Transfer Method (Lang, Ann. Bot. 

 xl, 1926, p. 710). Treat the exposed surface with a solution of 

 cellulose acetate in amyl acetate (or celloidin solution, or the trade 

 preparation " necol ") and allow the surface to dry thoroughly. 

 If necessary, repeat the treatment to obtain a strong film. Grind 

 away the superfluous rock, and place the specimen in hydro- 

 fluoric acid in a wax vessel until the cellulose film is free and clear 

 of mineral matter. Wash in water, dehydrate in 95 per cent, 

 alcohol (absolute alcohol must not be used). Clear in terpinol, 

 oil of bergamot, etc. (clove oil must not be used), and mount in 

 Canada balsam, applying slight pressure with a clip if necessary. 



See also Thoivias, Phil. Trans. Roy. Soc. Lond. B., ccxiii, 1925, 

 p. 299 ; Bolton, Ann. Bot., xliii, 1929, p. 414. 



The transfers may be examined by reflected light, a Leitz- 

 Wetzler vertical illuminator being useful in conjunction with high 

 powers (Walton). They are commonly rather opaque to trans- 

 mitted light. Infra-red photography (Walton, Nature, cxxxv, 

 1935, p. 265) yields very detailed pictures. Dixon [Nature, 

 cxxxv, 1935, p. 958) uses an Ultropak microscope with coal 

 material. 



1418. Fossil Pollen. A summary of the methods at present in 

 use is given by Godwin {New Phyt., xxxiii, 1934, p. 278). Peat 

 samples are treated with hot alkali, calcareous marls with hydro- 

 chloric acid, and the organic matter of the siliceous sediments is 

 obtained by decantation and treatment with hydrofluoric acid. 



For peat samples boil up a small amount with a few drops 

 of 10 per cent, caustic potash or caustic soda on a slide. 

 Examine the macerated material directly, or wash and mount in 

 glycerin jelly, either unstained or tinted with safranin. Modifica- 

 tions involve using known weights or volumes of peat, repeated 

 washings, centrifuging and making up in such a manner that a 

 known amount is present on each slide. Pressure on the coverslip 

 causes over-representation of large pollen grains, by squeezing out 

 smaller ones around the edge. 



Erdtmann's method {Svensk. Bot. Tids., xxvii, 1933) makes it 

 possible to examine samples too i)oor in pollen for the alkali 

 method. Mildly oxidise the sample with NaClO^ in a mixture of 

 acetic acid and sulphuric acid for some hours in the cold. Wash 

 the residue and dry it with acetone and ether. Then treat with 

 80 per cent, sulphuric acid, which hydrolyses the polysaccharide 



