PRACTICAL PROCESSES IN VEGETABLE HISTOLOGY. 69 
with acetic acid, which renders the protoplasm transparent, and 
then dissolves it. A concentrated solution of potash destoys it, 
but that attacks the nucleus as well. It is only employed to obtain 
a membranous skeleton of the tissue. 
Aleurone.—Sulphuric acid entirely destroys the grains of aleurone. 
Oily Matters.—The oily matters have a special refrangibility 
under the Microscope, which distinguishes them from other sub- 
stances inclosed in the tissues. ‘Their most general solvents are 
ether and the essential oils ; alcohol, chloroform, and benzene 
are also often used for this purpose. 
The oily matters which exisit in the solid state in plants, and 
which are known by the name of vegetable butters (cocoa-nut butter, 
cocoa butter, nutmeg butter, Japanese wax, palm-oil, laurel-oil, 
&c.), may be dissolved, like oily liquids, in ether and essential oils. 
The use of alcohol is often recommended to remove the oil 
from sections of the albumen, the embryo, or the cotyledons of 
oleaginous seeds ; we ought to call attention to the fact that ether 
acts more rapidly, and that moreover several oils are only partly 
soluble in alcohol, such as linseed-oil, hempseed-oil, poppy-oil, 
croton-oil, and nut-oil. 
Essential Oils.—Vhese oils are very unequally soluble in alcohol 
or ether ; they are all soluble in the fixed oils. They exist in the 
tissues in the condition of balsams or oleo-resins. ‘The non-volatile 
oils, in which the resinous substances are insoluble, allow of their 
extraction. 
But as the use of the fixed oils is inconvenient because of the 
difficulty of getting rid of them from the preparations which have 
been impregnated by them, we point out, according to Planchon,* 
the solubility and density of several essential oils, which it is useful 
to know in order to free the sections from them. 
A. Essential oils denser than water :—Bitter almonds, cloves, 
mustard, cinnamon. 
B. Essential oils less dense than water :— 
Camphor. 
Essence of roses, soluble in sulphuric acid. 
Essential oil of aniseed: when sulphuric acid is added to it in 
sufficient quantity the solution separates into two layers, of which 
only one is fluid. 
Essential oils of conifers, only soluble in several times their 
volume of alcohol. 
Essential oil of lavender, soluble in one volume of alcohol. 
Essential oil of rosemary, mint, and thyme, very soluble in 
alcohol. 
* Planchon, ‘Traité pratique de la détermination des drogues simples 
d’origine végétale,’ ii. 
