GENERAL TECHNIQUES FOR CLASSES OF PLANTS 697 



and briiiffs out the striations in the sheath. Examine in the 

 picric acid solution or remove after one to two minutes to water. 

 The sheath begins to disintegrate in a few hours. 



1382. Wall Structure of Heterokontae, etc. Swell with strong 

 caustic potash and stain with Congo red, or separate the portions 

 by treatment with cold or warm 30 per cent, aqueous chromic 

 acid. 



For clearing use chloral hydrate when mounting in non-resinous 

 media. Sodium hypochlorite is also good for dense parts, but its 

 action is too violent for very delicate structures. Hydrogen 

 peroxide is good for some very dense Phaeophyceoe (Higgin's, 

 Ann. Bot., xlv, 1931, p. 345). 



KuPFERATH (C. B. Soc. BioL, xciv, p. 408) uses antiformin to 

 reveal the structure of hard parts of alga?, the mixture being 

 cleared by the addition of 10 to 25 per cent. acid. The method 

 is especially useful with diatom frustules. 



1383. Wall Structure of Bacillariales (Diatoms). The cell 

 contents are removed by boiling in macerating liquids, especially 

 mineral acids, or by heating on a slide to carbonise the cell con- 

 tents. Delicate forms require more gentle treatment. Store 

 frustules in 50 per cent, alcohol. 



To Mount. Replace the alcohol with distilled water, shake 

 and place a drop of material on a coverslip spreading it evenly. 

 Allow the covers to dry and then heat to drive off any water in the 

 frustules. Add a drop of thin xylol balsam on a slide and warm 

 until firm. Special highly refractive media are often used. 

 Conger {J. Boy. Micr. Soc, 1925, p. 43) uses styrax or piperine 

 (/x = 1-68). 



Dry Mounts. Prepare cells by making several superposed 

 rings of cement on a slide. Invert a prepared coverslip, with 

 frustules dried as above, while warm so that the edge of the slip 

 lies on the cement ring. Press the cover slightly and evenly into 

 the ring so that it adheres well. Allow to cool and give a coat of 

 rather thick cement. 



1384. Selected diatoms may be isolated from strewn covers by 

 a mechanical linger attached to the microscope. The free tip of 

 the finger is slightly greased to make it sticky. The diatom is 

 redeposited on another coverslip in the centre of which is a thin 

 smear of gelatin dissolved in glacial acetic acid. Gently breathe 

 on the slide to cause the diatom to stick to the gelatin. The 

 specimen may be manipulated as desired by the mechanical 

 finger. Dry and mount as usual. 



Conger (J. Boij. Micr. Soc, 1925, p. 43) finds that material is 

 more easily withdrawn from a fine-grained, ground-glass slide 

 rather than a polished one. 



See also Caballero, J. Boy. Micr. Sac, Ixviii, 1927, p. 9. 



Murray (J. Boy. Micr. Soc, Lond., xlviii, 1928, p. 1) demon- 



