638 SUMMABY OF CUEBENT BESEABCHES BELATING TO 



gold-yellow tint, as after treatment with aniline chloride and hydro- 

 chloric acid. 



In working with sulphuric acid the fresh material is first cut 

 in water. A section having been taken up with a platinum spatula, 

 and the excess of water removed by blotting-paper, a drop of strong 

 sulphuric acid is placed upon it, and allowed to act for a short 

 time, usually a few seconds. The section is then plunged into water 

 and rapidly washed. After several washings it may be stained and 

 mounted. As a staining reagent, either Hoffmann's violet or prefer- 

 ably Hoffmann's blue may be used. In the former case the section 

 is quickly stained, washed in water, and then placed for twenty-four 

 hours or more in dilute glycerin, which dissolves out a great portion 

 of the dye from the stained cell-wall, and at the same time removes 

 the peculiar staining of the pits, which, if allowed to remain, is apt 

 to lead to very delusive results. The section is finally mounted in 

 glycerin. When Hoffmann's blue is used, a moderate quantity of 

 the dye is dissolved in a 50 per cent, solution of alcohol to which 

 have been added a few drops of acetic acid. After staining, the 

 sections are washed with water and mounted in glycerin. Or a suffi- 

 cient quantity of the dye may be dissolved in a 50 per cent, solution 

 of alcohol which has been saturated with picric acid, until the solution 

 assumes a dark greenish-blue tint. To this solution Gardiner gives 

 the name picric-Hoffinann's-blue. After staining, the sections are 

 washed with water and mounted in glycerin as before ; or, after treat- 

 ment with alcohol, they may be cleared with oil of cloves and mounted 

 in Canada balsam. 



In Tangl's method, sections of endosperm were stained with iodine 

 and mounted in chlor-zinc-iod. In such dry tissue as ripe endo- 

 sperm cells the cell-walls do not turn blue, but merely remain stained 

 with the ordinary yellow-brown due to iodine. The protoplasm, on 

 the other hand, assumes a very dark brown coloration, and after 

 some time there comes into view a series of strise traversing the 

 thickened cell- wall, which, from their coloration, and from the 

 fact that their depth of staining varies pari passu with that of the 

 protoplasm, are taken to be essentially protoplasmic in character. 

 Although in cases where it can be applied this method is of great 

 value, it is attended also vrith some disadvantages. Firstly, in tissues 

 containing a higher percentage of water the walls assume the ordinary 

 cellulose blue, which at once prevents the threads from being seen ; 

 and, secondly, on account of the extensive and varied staining pro- 

 perties of the iodine, the results obtained by it alone cannot be taken 

 as entirely conclusive. But, v^here practicable, Tangl's method is 

 of great use in giving at least an idea of the existence of the proto- 

 plasmic threads, and the staining of the threads with iodine is much 

 more distinct than with any other reagent. 



To obviate these difficulties Gardiner adopted the modification 

 already described of dissolving Hoffmann's blue in a 50 per cent, 

 solution of alcohol saturated with picric acid ; and, on washing out, 

 the threads were found to be well stained, the picric acid bodily 

 carrying, as it were, the solution of the dye into the fine protoplasmic 



