PLANT PRODUCTS 571 



Leucin, CsHioNHrCOOH. Leucin belongs to the amido-compounds. , It has 

 been found in etiolated leaves of Paspalum elegans and Dahlia veriabilis, and 

 associated with asparagin in seedlings of various Leguminosae, particularly in those 

 of lupinus. Leucin crystallizes in thin plates, which are lighter than water and have 

 the appearance of mother-of-pearl. If sections containing leucin are carefully 

 heated on a slide under a cover-glass to a temperature of I7OC., the cover-glass 

 will become covered with minute, scale-like crystals, which are doubly refractive 

 and may be studied to advantage by means of the polarizer. The crystals of leucin 

 may also be obtained if sections are treated with alcohol under a cover-glass, and 

 the alcohol is then allowed to evaporate slowly. 



Leucoplasts. For methods of fixing and staining leucoplasts, see in the last 

 chapter under Acid Puchsin, Gold Chloride, and Picronigrosin. 



Lignified Membranes. Dignified membranes are distinguished from cellulose 

 membranes by their insolubility in cuprammonia and by being colored from yellow 

 to brown by iodine or chloroiodide of zinc. One of the most reliable tests for ligni- 

 fied membranes will be found in the last chapter under Phloroglucin. Aniline sul- 

 phate is also a good test for lignified membranes. The sections are first mounted 

 in a drop of a concentrated solution of aniline sulphate, and then this is replaced 

 by a drop of concentrated sulphuric acid. By this treatment lignified membranes 

 are stained a golden yellow. See also under Double Staining in the last chapter. 



Lipochromes. These are yellow and red pigments which are for the most part 

 dissolved in fatty substances within the cells, and which are colored blue by sul- 

 phuric or nitric acid, and green by potassium iodide-iodine. 



Magnesium. To demonstrate the presence of magnesium within plant tissues, 

 sections are placed on the slide in a drop of sodium phosphate or sodium-ammonium 

 phosphate, and a little ammonium is added. In the presence of magnesium, 

 crystals of ammonio- magnesium phosphate are then formed, which have a coffin- 

 lid form. When the ash of tissues containing magnesium is treated as above, the 

 crystals are apt to form in x- or *- shaped groups. 



Maltose. Maltose is a sugar which is produced from starch by the action of 

 diastase. Maltose reduces Fehling's solution, but only about two-thirds as much 

 as grape-sugar (dextrose, glucose). 



Morphine, CnHigNOa. When the latex containing morphine is treated with 

 potassium iodide-iodine, a reddish-brown precipitate is produced, with potassium- 

 bismuth iodide a reddish-orange, and with potassio- mercuric iodide a yellowish- 

 white precipitate, while phospho-molybdic acid produces a yellow precipitate. 

 A solution of 5 drops of methylal in i mil of concentrated sulphuric acid gives 

 a violet color to latex containing morphine. 



Mucilages (see also under Gums). Mucilage contained in sections of plant 

 tissues may be differentiated by staining with methylene-blue. The sections may 

 be mounted on the glass slip in a drop of a solution of 0.4 Gm. of methylene-blue 

 in 100 mils of equal parts of water, glycerine, and 95 per cent, alcohol. The mucilage 

 will be seen under the microscope to be stained more deeply blue than the cell- walls 

 or other cell contents. If the sections are taken from fresh materials, the razor 

 should be moistened with alcohol. Dry materials should be soaked in water to 

 soften for cutting. If it is found that the mucilage dissolves too much in the 

 water, the mucilage may be hardened and the tissues softened at the same time 

 in the lead acetate solution described under Gums. 



Mustard Oil, C S H 6 CNS. Seeds and the vegetable organs of the Cruciferae, 

 Resedaceae, Capparidaceae, Tropaecolaceae, and Lemnanthaceae contain peculiar 

 nitrogenous glucosides which become decomposed into sulphur-bearing substances, 

 long known as mustard oils, by means of the enzyme myrosin. 



