PLANT PRODUCTS 577 



potassium hydrate, they assume a yellow color, which changes to orange on warming. 

 This reaction loses some of its value, however, from the fact that a glucoside called 

 sinalbine also occurs in the seeds of the white mustard and turns yellow on the 

 application of potassium hydrate. 



Solanin, C42H7 B NOi5. This glucoside occurs in the tissues of Solanum tuberosum. 

 To demonstrate its presence, sections should be placed in a mixture of i part of 

 ammonium vanadate and 1,000 parts of a mixture of 98 parts of sulphuric acid with 

 36 parts of water. This produces with solanin a yellow color, which changes 

 successively into orange, purple-red, brown, red-orange, carmine-red, raspberry- 

 red, and blue-violet. The color then passes into a grayish-blue and disappears. 

 With concentrated sulphuric acid solanin assumes a yellow color, which changes 

 to red, and then violet, and then passes into gray and disappears. 



Spergulin, CsHyOz. This occurs in the seed coats of species of Spergula. It is 

 soluble in alcohol with a blue fluorescence, in ether, and in concentrated sulphuric 

 acid with a deep blue color. It is insoluble in chloroform, benzine, and in the fatty 

 and ethereal oils. When caustic potash is added to an alcoholic solution of sper- 

 gulin, an emerald-green fluorescence is produced. 



Starch, CeHioOs. A solution of potassium iodide stains starch from pale violet 

 to purple, depending on the strength of the iodine solution. Chloroiodide of zinc 

 stains starch-grains purple, and at the same time swells them. A solution of chloral 

 hydrate and iodine dissolves the protoplasmic cell-contents and stains included 

 starch-grains purple. This reagent is particularly adapted to demonstrate the 

 presence of starch in chloroplasts or amyloplasts. The bleaching effect of the 

 chloral hydrate is so great that starch may be demonstrated in whole leaves by the 

 chloral hydrate and iodine reagent. For the further treatment of starch with 

 reagents, see in the preceding chapter under Eau de Javelle, Calcium Nitrate, 

 Diastase, Methyl-violet, Silver Nitrate. 



Strychnine, CziHzaNzC^. When sections containing strychnine are treated 

 with a solution of i Gm. of ammonium vanadate in 100 mils of sulphuric acid, they 

 quickly take on a violet-red color, which after a time changes to brown. If sections 

 of the seeds of Strychnos nux-vomica are treated with sulphuric acid containing an 

 excess of eerie sulphate, the walls of the cells are colored a bluish-violet. The 

 sections must have been previously treated with petroleum ether and absolute 

 alcohol to remove the fatty oils, grape-sugar, and brucine. The reagent should be 

 applied immediately before the observation is to be made. If sections are treated 

 with concentrated sulphuric acid, and crystals of potassium bichromate are then 

 added, a violet color is produced. 



Suberin and Suberized Walls. Suberized walls are stained green when treated 

 for about an hour in the dark by a freshly-prepared strong "solution of chlorophyll. 

 A cold concentrated solution of potassium hydrate colors suberized walls yellow. 

 When the potassium hydrate is heated yellow drops and granular masses are 

 formed. When suberized walls are heated in a solution of potassium chlorate in 

 nitric acid, they become changed into droplets which melt between 30 and 40 C., 

 and which are soluble in hot chloroform, alcohol, ether, benzol, or dilute potassium 

 hydrate. At ordinary temperatures concentrated chromic acid solutions have 

 little effect on suberized walls. A solution of potassium iodide-iodine and chloro- 

 iodide of zinc colors suberized membranes from yellow to brown. After long treat- 

 ment with a dilute solution of potassium hydrate, suberized membranes may be 

 stained violet with chloroiodide of zinc. Alcannin stains suberized walls red. 

 Under the polariscope suberized walls are seen to be doubly refractive. They lose 

 this property on heating and regain it on cooling. It may be deduced from this 

 that the constituents of the walls are in part, at least, in crystals which are melted 

 by heat, but reappear on cooling. See under Methyl-blue and Double Staining. 



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