340 MICROCHEMISTRY OF PLANT PRODUCTS 



chlorophyll; it occurs in crystalline form in the roots of carrots, 

 which have a yellow color in consequence. To demonstrate 

 the presence of carotin in chloroplasts place pieces of fresh 

 leaves in a 20 per cent, solution of potassium hydroxide in 40 

 per cent, alcohol, and leave them thus in a tightly closed vessel 

 for several days. When the chlorophyll has been extracted 

 from the leaves, they should be washed in distilled water and 

 sections from them should be mounted in glycerine. Yellowish 

 and red crystals will then be found in the cells which formerly 

 contained chlorophyll. Carotin is insoluble in water and with 

 difficulty in alcohol, but is readily soluble in petroleum ether, 

 benzol and benzine. When freshly dried leaves or roots of 

 carrots are powdered and treated with one of these solvents, 

 and the solution is allowed to dry or it is treated with alcohol, 

 carotin crystallizes out in the form of reddish or yellowish crys- 

 tals. With a solution of iodine carotin is colored greenish or 

 bluish; with concentrated sulphuric acid it is colored from violet 

 to indigo-blue. 



Cellulose, CgHj^O^. — Cellulose is one of the most impor- 

 tant constituents of cell-walls; the first-formed walls are nearly 

 always of cellulose, together with certain pectic compounds. 

 Modified cell-walls — namely, those which have become cutin- 

 ized or lignified — have arisen by the chemical modification of 

 cellulose, or by the infiltration of new material between the 

 cellulose molecules, or by both of these processes. Cellulose 

 is characterized by being soluble in sulphuric acid and cupram- 

 monia; by being colored from violet to blue by sulphuric acid 

 and iodine, chloroiodide of zinc, chloroiodide of calcium, iodine 

 and aluminum chloride, iodine and phosphoric acid. See under 

 these heads in the chapter on Reagents. 



Chitin. — The chemical composition of chitin is not pre- 

 cisely known, but it has been estimated to be CjgHggNjO^,- 

 The walls of many fungi consist of chitin instead of cellulose. 

 This may be demonstrated by cutting the pileus of an Agaricus 

 into small pieces, which are then to be treated successively 

 with dilute potassium hydrate, dilute sulphuric acid heated 



