128 
METHODS IN PLANT HISTOLOGY 
may be used in addition. Living material may be fixed in a mixture 
of picric 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. Desifilication, etc. —Silica and other mineral deposits are 
removed by treating with a 10 per cent aqueous solution of com¬ 
mercial hydrofluoric acid. The material is tranferred to this solu¬ 
tion 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 
celloidin: 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 per cent. Transfer 
from absolute 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° to 60° C. for 12 to 
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 solutions, may be used repeat¬ 
edly), 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 few chips of dry celloidin 
from time to time until the mixture is quite stiff and firm. Remove 
each block with the celloidin adhering to it and harden it in chloro¬ 
form for 12 hours. Then transfer to a mixture of equal parts of 
glycerin and 95 per cent alcohol, where the material should remain 
for a few days before cutting. 
Cutting, Staining, and Mounting. —Although 10 ix is usually thin 
enough, sections are readily cut as thin as 5 /jl by this method. 
