570 ELEMENTS OF PLANT HISTOLOGY AND MICROTECHNIC 



microscope. For directions for staining and making permanent preparations of 

 sections containing mucilages and gums see under Boric Acid in the preceding 

 chapter. 



Hemicelluloses. These are reserve materials which are deposited as additions 

 to the cell-walls in the endosperm of seeds and in wood parenchyma and wood- 

 fibers. By means of enzymes they may be converted into gums and sugars, in 

 which forms they may be transported to those parts where growth is taking place. 

 The hemicellulose or reserve cellulose in the endosperm of the date seed acts like 

 ordinary cellulose in being colored blue by chloroiodide of zinc and in dissolving 

 in cuprammonia. The reserve cellulose in the endosperm of the seeds of Lupinus 

 luteus is not dissolved in cuprammonia, and does not assume a blue color when 

 treated with chloroiodide of zinc. 



Hesperidin, CnHjeOu. This glucoside occurs dissolved in the cell-sap of 

 many plants. It may be precipitated from its solution in the cell-sap by means 

 of alcohol. The precipitate is in the form of crystals, which are colorless or slightly 

 yellow,' and are doubly refractive, so that they may be studied to good advantage 

 by means of the polarizer. Hesperidin is also precipitated on the drying up of the 

 cell-sap. The crystals of hesperidin are insoluble in cold and boiling water, alcohol, 

 ether, benzine, and dilute acids, but they are soluble in solutions of caustic potash 

 and soda, and in ammonia, yielding a yellowish color to the solvent. Hesperidin 

 may readily be obtained for study in the unripe fruit of the orange and in the epi- 

 dermal cells of Capsella bursa-pastoris. Hesperidin may become deposited in the 

 form of spaerocrystals, when the tissues containing it have lain for some time in 

 strong alcohol or glycerine, acting in this respect similarly to inulin. The constitu- 

 ent acicular crystals of the hesperidin sphaerites can be more easily distinguished 

 than those of inulin, and when the hesperidin sphaerites are treated with a drop of 

 a-naphtol, and then with two or three drops of concentrated sulphuric acid, they 

 dissolve with a yellow color, while, with like treatment, inulin sphaerites dissolve 

 with a violet color. 



Indican. The glucoside indican is a substance of the consistency of syrup, and 

 of a yellowish or brownish color. It is found in Isatis tinctoria, Phajus grandifolius 

 and in other indigo-bearing plants. When tissues containing indican are exposed 

 to the air, they may take on a blue color due to the conversion of the indican to 

 indigotin, which may be precipitated in alcohol in the form of small, tabular, 

 bluish crystals. To demonstrate the presence of indican, tissues containing it 

 should be placed under a bell-jar and over a dish of absolute alcohol. After stand- 

 ing exposed to the vapor of alcohol for 24 hours, the tissues will be colored blue by 

 the indigo blue which will have been forced from the indican. A piece of moistened 

 filter-paper should be placed under the bell-jar to keep the tissues from drying. 



Inulin, Ci2H2oO 1 o. Inulin is a carbohydrate which occurs dissolved in the cell- 

 sap of many plants, particularly among the Composite. It may be deposited from 

 its solution in the cell-sap by means of alcohol. To study the sphaerocrystals 

 of inulin, pieces of dandelion or dahlia roots should be placed in 50 per cent, 

 alcohol for a week or more, and then thin sections should be prepared and ex- 

 amined in a drop of the alcohol under the microscope. The sections should 

 not be placed in water, since the crystals of inulin are soluble in it. The sphaerites 

 will appear applied to the walls of the cells. When the alcohol is replaced by water 

 which is then heated over a flame, the sphaerites will dissolve. If sections con- 

 taining inulin sphaerites are treated with a 20 per cent, solution of a-naphthol, 

 and then 2 or 3 drops of concentrated sulphuric acid are added, the sphaerites 

 will be seen to dissolve with a violet color. Inulin does not reduce Pehling's 

 solution. 



