REAGENTS. 



807 



days, filtered, and then 100 c.c. each of glycerin and methyl alco- 

 hol are added, the solution allowed to stand for several days and 

 finally filtered. An excess of the stain is removed from the sec- 

 tions by subsequent washing either with a 2 per cent, alum solu- 

 tion or an acidified alcoholic solution. This solution gives to 

 cellulos,e, lignin and the protoplasmic cell contents a violet color. 



B 



Fig. 325. Diagrams showing the difference between an air- bubble and an oil-globule 

 in different foci; When the focus is above, as at A, the air-bubble (C) is dark gray and 

 the oil-globule (E) light gray. When the focus is at the lower portion, as at B, the air- 

 bubble (D) is light in the center and the oil-globule (F) dark gray. The same optical effects 

 as are obtained with oil-globules are observed with cell walls, starch grains and crystals. 



Iodine and Potassium-Iodide Solution consists of iodine, 

 13 Gm. ; potassium iodide, 20 Gm. ; water, 100 c.c. 



Iodine Water is prepared by adding as much iodine to dis- 

 tilled and sterilized water as it will dissolve (about 1:5,000). 



Chloral-Iodine Solution consists of a saturated aqueous 

 solution of chloral, to which iodine is added. This reagent is 

 useful for staining the starch grains in the chloroplasts. 



