136 METHODS IN PLANT HISTOLOGY 



Jeffrey's improvements in the celloidin method have been de- 

 scribed in considerable detail by Plowman. ^ Sections of hard stems 

 and roots cut by this method could hardly be surpassed, and they are 

 perfectly adapted to the requirements of photomicrography. The fol- 

 lowing is a brief abstract of Plowman's paper: 



1. Preparation of material. — Dead and dry material should be re- 

 peatedly boiled in water and cooled to remove air. An air-pump may 

 be used in addition. Living material may be fixed in a mixture of pic- 

 ric acid, mercuric chloride, and alcohol: 



Mercuric chloride, saturated solution, in 30 per cent alcohol. 3 parts 

 Picric acid, saturated solution, in 30 per cent alcohol 1 part 



Fix 24 hours, and wash by passing through 40, 50, 60, 70, and 80 per 

 cent alcohol, allowing each to act for 24 hours. 



2. Desilification, etc. — Sihca and other mineral deposits are re- 

 moved by treating with a 10 per cent aqueous solution of commercial 

 hydrofluoric acid. The material is transferred to this solution from 

 water or from the 80 per cent alcohol. The process may require 3 or 4 

 days, with one or two changes of the acid and frequent shaking of the 

 bottle. An ordinary wide-mouthed bottle, coated internally with hard 

 paraffin, should be prepared, since the acid is usually sold in bottles 

 with narrow necks. The bottles are easily prepared by filling them 

 with hot paraffin and simply pouring the paraffin out. Enough will 

 stick to the bottle to protect the glass from the acid. Wash in running 

 water 3 or 4 hours. 



3. Dehydration.— Use 30, 50, 70, 90, and 100 per cent alcohol, 

 allowing 12 hours in each grade. 



4. Infiltration with celloidin. — There should be ten grades of celloi- 

 din: 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 per cent. Transfer from abso- 

 lute alcohol to the 2 per cent celloidin. (We should prefer a previous 

 treatment with ether-alcohol.) The bottle should be nearly filled, and 

 the stopper should be clamped or wired in place. Put the bottle on its 

 side in a paraffin bath at 50°-60° C. for 12-18 hours. Cool the bottle 

 quickly in cold water, taking care that the water does not get into the 

 bottle. Pour out the 2 per cent solution (which, as well as all other so- 

 lutions, may be used repeatedly), and replace it with the 4 per cent, 

 and proceed in the same way with the other grades. When the 20 per 

 cent solution is reached, a further thickening is gained by adding a 



1 A. B. Plowman, "The Celloidin Method with Hard Tissues." Botanical Gazette, 

 37:456-461, 1904. 



