354 MICROCHEMISTRY OF PLANT PRODUCTS 



Oils. — Ethereal and fatty oils have already been discussed 

 under separate heads, where the methods for distinguishing 

 between the two will be found. See also in the last chapter 

 under Alcannin, Cyanin, and Osmic Acid. 



Oxalic Acid. — When calcium nitrate is added to sections 

 containing oxalic acid, crystals of calcium oxalate are formed. 

 With uranyl acetate crystals of uranium oxalate are formed 

 in tissues containing oxalic acid. The crystals are rhombic, 

 of rectangular form, and when large, appear of a yellow color, 

 and, being doubly refractive, they may be studied to advantage 

 with the polarizer. 



Paragalactan. — This occurs as a thickening of the cell-walls 

 in the cotyledons of Lupiniis luteus. When it is heated with 

 nitric acid, mucic acid is formed, and when heated with dilute 

 sulphuric acid, galactose, CgHj^Og, and a pentaglucose are 

 formed. When heated with phloroglucin and hydrochloric 

 acid, a cherry-red color is produced. Paragalactan is not dis- 

 solved by cuprammonia, and is stained slightly or not at all 

 by chloroiodide of zinc. 



Paramylum. — Paramylum grains are flattened, cylindrical, 

 stratified bodies occurring in the bodies of the Euglense and in 

 the cysts of Leptophrys vorax. The paramylum grains are 

 hardly affected by water, alcohol, ether, nitric acid, or concen- 

 trated chromic acid; and while they are hardly soluble in 5 

 per cent, potassium hydrate, they are easily soluble in a 6 per 

 cent, solution. They may also be dissolved in concentrated 

 sulphuric acid. They are not stained by iodine, chloroiodide 

 of zinc, or by any of the organic coloring matters. 



Pectic Compounds. — The pectic substances (pectin, pec- 

 tose, and pectic acids) are widely distributed in the membranes 

 of plants. Pectose occurs associated with cellulose in the mem- 

 branes of embryonic tissues, where it is distributed throughout 

 the entire thickness of the membrane. Pectose also occurs 

 in most lignified, suberized, and cutinized membranes. The 

 middle portion of cell-walls — the so-called middle lamella — 

 consists, for the most part, of calcium pectate. When thin 



