REAGENTS AND PROCESSES 533 



what longer time in carmalum. By this treatment lignified membranes are stained 

 by the iodine green, while the unlignified membranes are stained by the carmalum. 



Cedar Oil. Sections which are to be mounted in balsam may first be examined 

 in cedar oil to determine their fitness for permanent mounts; if they are satisfactory, 

 the cedar oil may be drained off and the balsam immediately added to the slide. 

 Cedar oil has a clearing effect on sections which are treated with it. 



Thicker cedar oil with a refractive index of about 1.515 is used as an immersion 

 fluid for homogeneous immersion lenses. 



Cedar oil is often used as an intermediary between alcohol and paraffin in paraf- 

 fin-imbedding, but for plant tissues chloroform is rather to be recommended. 



Celloidin. See Steven's Plant Anatomy, pages 233-235. 



Chloral Carmine. This is useful in clearing pollen-grains and staining their 

 nuclei at the same time. It is prepared as follows: Carmine 0.5 Gm. and 30 drops 

 of officinal hydrochloric acid (specific gravity, 1.13 or 17 B.) are added to 30 mils 

 of alcohol, and this is heated for about thirty minutes on the water-bath; then, after 

 cooling, 25 Gm. of chloral hydrate are added, and the solution is filtered until clear. 



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

 chloral hydrate may be taken in grams and the water in mils. This is one of the 

 best clearing agents. Whole leaves, when boiled in this solution, clear quickly to 

 such an extent that they may be studied by transmitted light throughout all of the 

 cell-layers. Crystals in leaves may be plainly demonstrated in this way. This 

 reagent is also very useful in clearing pollen-grains and embryos within the 

 ovules. 



Chloral Hydrate-iodine. Dissolve 5 parts of chloral hydrate in 2 parts of water 

 and add a small amount of potassium iodide-iodine. 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 paraffin in the process of imbedding in 

 paraffin. One of the best solvents of fatty oils and of carotin. Solvent of most 

 of the constituents of suberin. 



Chloroiodide of Zinc. Prepared by dissolving zinc in concentrated hydro- 

 chloric acid to saturation and then evaporating to the consistency of concentrated 

 sulphuric acid, adding as much potassium iodide as can be taken up, and then 

 crystals of iodine until no more is dissolved. Another method is to dissolve 20 

 parts of chloride of zinc, 6.5 parts of potassium iodine, and 1.3 parts of iodine in 

 10.5 parts 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 membranes. By it cellulose walls are colored violet, lignified membranes 

 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 wea.k 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 protoplasmic 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 chlorophyll solution for an hour or so in the dark, cutinized and sub- 

 erized membranes are stained green, while lignified and cellulose membranes re- 

 main unstained. The chlorophyll solution will not keep, and should be freshly 

 prepared whenever needed. 



