292 REAGENTS AND PROCESSES 



Chloral Hydrate-iodine. — Dissolve five parts of chloral 

 hydrate in two parts of water and add enough finely powdered 

 iodine to leave an excess undissolved after long standing. Shake 

 before using. This is the best reagent for demonstrating the 

 presence of starch in chlorophyll corpuscles and in pyrenoids, 

 or in any situation where the starch is surrounded and obscured 

 by other substances. 



Chloroform. — Used as a solvent for fatty oils and of caro- 

 tin. Used as a solvent for paraffin in the process of imbedding 

 in paraffin. See page 261. 



r Chloroiodide of Zinc. — Dissolve 30 gm. of chloride 

 [of zinc, 5 gm. of potassium iodide and 0.89 gm. of iodine 

 (in 14 c.c. of distilled water. Chloroiodide of zinc solutions 

 should be kept in the dark. This reagent is one of the most 

 generally useful in determining the character of plant mem- 

 branes. By it cellulose walls are colored violet, lignified mem- 

 branes a yellowish-brown, cutinized and suberized membranes 

 from yellow to yellowish-brown. When sections containing 

 sieve tubes are treated with chloroiodide of zinc and a rather 

 weak solution of potassium iodide-iodine, the walls of the 

 sieve tubes appear violet, while the pits in the sieve plates 

 are a reddish-brown, due to the strands of protoplasm which 

 penetrate them; the callose plates are stained a reddish-brown. 

 Mucilaginous walls are colored violet by this reagent. Chloro- 

 iodide of zinc stains protopla,smic cell-contents from yellow to 

 brown, and starch from purple to almost black. 



Chlorophyll Solution. — A freshly prepared strong solution 

 of chlorophyll in alcohol is used to demonstrate suberized and 

 cutinized membranes. When sections are kept in the chloro- 

 phyll solution for an hour or so in the dark, cutinized and sub- 

 erized membranes are stained green, while lignified and cellu- 

 lose membranes remain unstained. The chlorophyll solution 

 will not keep, and should be freshly prepared whenever needed. 



Chromic Acid. — Solutions of i per cent, and 0.5 per cent, 

 have been much used for fixing plant tissues. The material 

 to be fixed should lie in the chromic acid for a day or more, 



