2IO PART II. VEGETABLE HISTOLOGY. 



cuticularized tissues brown, when used in connection with iodine, but does not 

 dissolve them, hence it may be used as a test for them. Cells containing pro- 

 toplasm, if first treated with a solution of cane sugar and then afterward with 

 sulphuric acid, acquire a rose red color. 



Acetic Acid (Glacial). This acid, in two per cent, aqueous solution, is 

 serviceable for defining the nucleus ; when used strong, it is a valuable clearing 

 agent, dissolving the cell-contents and rendering the cell-walls more distinct, 

 and it is useful as a means of distinguishing between deposits consisting of 

 calcium carbonate and those composed of calcium oxalate or silica, since calcium 

 oxalate is dissolved by it with effervescence, while both of the other substances 

 are insoluble. 



Hydrochloric Acid. Besides its use in connection with phloroglucin and 

 aniline chloride in testing for lignin, it is more or less serviceable as a clearing 

 agent, and is useful in distinguishing between calcium carbonate and calcium 

 oxalate, both being soluble in this reagent, but the former with effervescence 

 and the latter more slowly and without effervescence. A one-fourth per cent, 

 solution of the acid in 70 per cent, alcohol is also serviceable in reducing the 

 color of sections which have been overstained in carmine or hsematoxylin solu- 

 tions. 



Cuprammonia. This is the only known reagent capable of dissolving 

 cellulose without producing chemical change in it. It is prepared by adding to 

 an aqueous solution of cupric sulphate an aqueous solution of sodic hydrate, 

 collecting the precipitate which forms, by allowing it to settle and decanting the 

 supernatant liquid, and dissolving it in ammonia. Pure cellulose tissues 

 readily dissolve in it, but lignified ones do not. The undiluted solution should 

 be used. 



Mercuric Chloride. Make a two per cent, solution of the crystals in 

 strong alcohol. It has the property of hardening albuminoid compounds and 

 rendering them insoluble in water. On this account it is used for the study of 

 aleurone grains. The sections to be studied should be soaked in the solution 

 for from twelve to twenty-four hours. They may then be stained and examined. 

 Specimens thus treated should not be handled with metallic forceps. 



Alcohol. Alcohol is one of the most indispensable of reagents in vegetable 

 histology. One important use it has is in the preservation of tissues. For this 

 purpose 70 per cent, alcohol has sufficient strength. But it is often desirable at 

 the same time to harden the tissues for section-cutting. For this purpose 

 strong alcohol, 95 to 98 per cent., is often necessary. If, however, the tissues 

 are very delicate, they must not be immediately placed in alcohol of this 

 strength, but gradually transferred to it through graduated solutions of increas- 

 ing strength. 



Alcohol also dissolves chlorophyll and other coloring matters together with 

 resinous substances, and so acts as a bleaching agent. Since it coagulates and 

 destroys the vitality of protoplasm, without seriously impairing its structure, it 

 is useful in preparing cells for the study of cell contents. Living protoplasm is 

 so transparent as to be nearly invisible, and it also refuses to take upmost 

 staining materials ; but after treatment with alcohol, it may readily be stained 

 with carmine, eosin, hematoxylin and various other solutions. 



