PLANT PRODUCTS 565 



sodium carbonate. The aniline blue should be used in dilute aqueous solutions, 

 in which the sections are to remain for about half an hour. Over-staining may be 

 remedied by washing out in glycerine. 



Calycin, CigHnOs. This occurs in the tissues of many lichens. Its presence 

 may be demonstrated by moistening some of the powdered lichen with glacial 

 acetic acid, and when the preparation dries, the long, doubly refractive crystals 

 of calycin are deposited. When a section of lichen containing calycin is treated 

 on the slide with a few drops of chloroform and a drop of sodium hydrate, that 

 portion of the section which contains calycin assumes a color varying from brick- 

 red to blue-red. 



Cane-sugar (Sucrose), C^H^On. This is of common occurrence in plant tis- 

 sues. At I5C. it is soluble in ^ part of water. It is difficultly soluble in alcohol. 

 When boiled with Fehling's solution, it does not at first precipitate cuprous oxide, 

 but on longer boiling it becomes converted into glucose and lasvulose, which are 

 capable of reducing Fehling's solution. If rather thick sections containing cane- 

 sugar (the sugar-beet affords good material) are placed for a short time in a con- 

 centrated solution of cupric sulphate, and then quickly rinsed in water, transferred 

 to a solution of I part of potassium hydrate in i part of water, and heated to 

 boiling, the cells containing the sugar take on a sky-blue color. A blue color is 

 also produced by Fehling's solution when sections containing canersugar are heated 

 in a drop of the solution on a slide until bubbles arise. 



Carotin, C 2 6H 38 . Carotin occurs in the orange and red chromatophores ot 

 many flowers and fruits; it seems also to be an essential part of chlorophyll; it 

 occurs in crystalline form in the roots of carrots, which have a yellow color in con- 

 sequence. 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 chloro- 

 phyll 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 is treated with alcohol, carotin crystallizes out in the form of 

 reddish or yellowish crystals. With a solution of iodine carotin is colored greenish 

 or bluish; with concentrated sulphuric acid it is colored from violet to indigo 

 blue. 



Cellulose, CeHioOs. Cellulose is one of the most important 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 cup- 

 rammonia; 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 walls of many fungi consist of chitin instead of cellulose. This 

 may be demonstrated by cutting the pileus of an agaracus into small pieces, which 

 are then to be treated successively with dilute potassium hydrate, dilute sulphuric 

 acid heated to boiling, alcohol, and finally ether. When this process is completed, 

 a white substance remains which becomes hard and horny on drying, and which is 

 insoluble to all reagents except concentrated acids, and in all other respects pos- 

 sesses the characteristics of chitin. 



