102 
METHODS IN PLANT HISTOLOGY 
Even after the method became established, there occurred a 
period of several years during which it was practically impossible 
to get a Venetian turpentine suitable for histological use. Conse¬ 
quently, it was necessary to resort to glycerin jelly or to try various 
schemes for bringing material into Canada balsam; but good Venetian 
turpentines have appeared again and are even more satisfactory 
than those which established the method in popular favor. We have 
tested two brands which are giving uniform and excellent results: 
these are the “Venice Turpentine (True),” sold by the Fuller- 
Morrison Company, of Chicago; and the “Turpentine Venetian” 
(No. 2605), sold by the National Anilin and Chemical Company, of 
New York. There are probably other good turpentines and still 
others are likely to appear. Venetian turpentine is made from the 
resin of Larix europea. Since this resin is soluble in absolute alcohol, 
material can be transferred directly from absolute alcohol to a thin 
solution of the mounting medium, without the intervention of xylol 
or any other oil, thus eliminating the most dangerous stage in the 
preparation of filamentous algae and fungi and any forms which are 
to be mounted whole. 
The general outline, just given, is not sufficiently definite for a 
working introduction. The following concrete examples, describing 
the use of Venetian turpentine with an aqueous stain, with an alcoholic 
stain, and with a combination of aqueous and alcoholic stains, 
will be more practical than general directions. The steps from 
fixing to mounting, as used with an aqueous stain, will be described 
first, since this will introduce the method in its least complicated 
form. 
Haidenhain’s Iron-Haematoxylin.—-Using Spirogyra as a type, 
proceed as follows: 
1. Fix 24 hours in chromo-acetic acid. 
1 per cent chromic acid. 100 c.c. 
Glacial acetic acid. 3 c.c. 
The volume of the fixing agent should be at least 50 times that of 
the material to be fixed. 
2. Wash in running water 10 hours; if running water is not available, 
24 hours, changing often. 
3. 2 per cent aqueous solution of iron-alum (ammonia sulphate of iron), 
2 hours. 
4. Wash in running water, 20 minutes. If running water is not avail¬ 
able, wash in a large quantity of water and change frequently. 
