ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 749 



Sections made transversely to the saccharine tissues can also be 

 allowed to dry. In evaporating, the cell-sap leaves the saccharoses 

 in the form of stellate crystals, the crystallographic system of which 

 it then becomes possible to recognize. 



Aleurone. — This is the place to point out the means of preserving 

 from solution in water the proteid part of the aleurone grains. It is 

 known that in several plants, the peony for instance, this portion of 

 the grain is very soluble in water. It is rendered insoluble by first 

 subjecting it to the action of an alcoholic solution of bichloride of 

 mercury. It is on this very phenomenon that Pfeffer relies to estab- 

 lish the presence of a quaternary nitrogenous substance in the aleurone 

 grain.* 



V. Dissolution and Destruction. 



We dissolve certain substances either with the object of discover- 

 ing what they are, or more freq[uently the better to see the elements 

 which they hide. Thus it is not uncommon to destroy the protoplasm 

 in order to make the nucleus more visible. 



Protoplasm. — In order to display the nucleus, the tissue is treated 

 with acetic acid, which renders the protoplasm transparent, and then 

 dissolves it. A concentrated solution of potash destroys it, but that 

 attacks the nucleus as well. It is only employed to obtain a mem- 

 branous 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 substances in- 

 closed in the tissues. Their most general solvents are ether and the 

 essential oils; alcohol, chloroform, and benzine are also often used 

 for this purpose. 



The oily matters which exist in the solid state in plants, and 

 \vhich 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. — These 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,f the 



* Pfeffer, Jahrb. f. Wiss. Botanik, viii. (1872). 



t Planchon, ' Traite pratique de la de'termination des drogues simples 

 d'origine vege'tale,' ii. 



Ser. 2.— Vol. III. 3 D 



