572 ELEMENTS OF PLANT HISTOLOGY AND MICROTECHNIC 



Myrosin. Myrosin is an enzyme occurring in certain specialized cells in the 

 seeds and other parts of many Crucif eras. The cells containing myrosin are stained 

 a deep red by Millon's reagent, while the surrounding cells may be stained a pale 

 rose color. When sections containing myrosin are heated in a concentrated solu- 

 tion of hydrochloric acid which contains a drop of a 10 percent, aqueous solution 

 of orcin in each mil, a violet color is produced in the cells containing the myrosin. 

 Myrosin produces allylic mustard oil from potassium myronate, a glucoside 

 occurring in the parenchyma cells which are associated with those containing 

 myrosin. 



Narceine, CjsH^NOj. This is an alkaloid occurring in the latex of Papaver 

 somniferum. When a yellow color follows the addition of methylal to the latex, 

 the presence of narcelne is indicated. 



Narcotine, CszHzjNO?. Sodium selenate produces an orange-red color with the 

 latex of Papaver somniferum, indicating the presence of narcotine. 



Nicotine, CioHuNj. When sections containing nicotine are treated with 

 potassio-mercuric chloride, a yellowish-white precipitate is produced. Phospho- 

 molybdic acid gives, with nicotine, an abundant yellow precipitate. In the pres- 

 ence of nicotine mercuric chloride produces a white, and platinum chloride a yellow, 

 precipitate, while potassium iodide-iodine causes first a carmine-red color and 

 finally a reddish-brown precipitate, which gradually bleaches out. 



Nitrates. When nitrates are present in a solution, a drop of barium chloride 

 added to a drop of the solution will produce a precipitate of octahedral crystals of 

 barium nitrate. See also under Diphenylamine in the preceding chapter. 



Nucleus. The nucleus can best be demonstrated in tissues which have been 

 fixed according to the directions given under Fixatives in the last chapter. Also 

 under Iodine-green and Acetic Acid, and Methyl-green and Acetic Acid, are given 

 directions for instantly fixing and staining nuclei. The three-color method of 

 staining detailed on page 537 gives the best results for the dividing nucleus. 



Oils. Ethereal and fatty oils have already been discussed under separate heads, 

 where the methods for distinguishing the two will be found. See also in the 

 preceding 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 Lupinus luteus. When it is heated with nitric acid, mucic acid is formed, and 

 when heated with dilute sulphuric acid, galactose, CeHiaOe, and a pentaglucose 

 are formed. When heated with phloroglucin and hydrochloric acid, a cherry-red 

 color is produced. Paragalactan is not dissolved 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 Euglenae and in the cysts of Leptophrys vorax. The 

 paramylum grains are hardly affected by water, alcohol, ether, nitric acid, or 

 concentrated chromic acid; and while they are hardly soluble in 5 per cent, potas- 

 sium 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, chloro- 

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



Pectic Compounds. The pectic substances (pectin, pectose, and pectic acids) 

 are widely distributed in the membranes of plants. Pectose occurs associated with 



