CHAPTER XX. 

 REAGENTS AND PROCESSES. 



Chloral Hydrate. Dissolve 8 parts of chloral hydrate in 5 parts of 

 distilled water, namely, in the proportion of 8 grams of chloral hydrate 

 to 5 grams or 5 cubic centimeters of distilled water (since i cubic centi- 

 meter of distilled water weighs i gram). Used to clear plant tissues, or, 

 in conjunction with iodine, to demonstrate the presence of starch in 

 leaves, etc. (See Chloral Hydrate-Iodine.) Whole leaves and thick 

 sections can be very quickly cleared by boiling in this solution. 



Chloral Hydrate-Iodine. Dissolve 5 parts by weight of chloral 

 hydrate in 2 parts by weight of a weak solution of iodine. (See Iodine 

 Solution.) 



In using this reagent as a test for starch in thin sections of leaves, 

 etc., mount the section in a drop of water under a coverglass ; focus 

 the section with a high-power objective ; place a drop of the solution on 

 the glass slip in contact with the edge of the coverglass, and place a 

 piece of filter paper in contact with the opposite side of the coverglass. 

 In this way the solution will be drawn under the coverglass, and its 

 progressive action in clearing the section and staining the starch can be 

 followed. 



Chloroiodide of Zinc. (Chlor-zinc iodide.) Dissolve zinc to satura- 

 tion in concentrated hydrochloric acid and evaporate the solution to the 

 consistency of concentrated sulphuric acid. Add potassium iodide to 

 saturation, and then as much iodine as can be taken up. The solution 

 should have a decidedly reddish brown color. 



Since only a small quantity of this reagent is likely to be needed, it is 

 perhaps best to buy it ready prepared, from dealers in microscope sup- 

 plies. It should be kept in the dark, well stoppered. By this reagent 

 cellulose membranes are stained violet to purple. Starch is stained the 

 same color and swollen. Lignified, corky, and cutinized membranes are 

 stained a golden yellow. Proteid cell contents and protoplasts are 

 stained yellow to brown. It can be used in connection with phloro- 

 glucin, as described under that reagent. 



