MICRO-CHEMICAL REAGENTS. 



IODINE. 



THIS is one of the most valuable and indis- 

 pensable substances used in microscopic botany. 

 It is employed in solution, either in water, 1 alcohol, 

 or a solution of potassic iodide in glycerine, chlpr- 

 iodide of zinc, or water. The degree of concentra- 

 tion of the solution depends upon the particular 

 case in which it is to be used, the effects of much- 

 diluted solutions being often very evident. For 

 the recognition of starch, iodine is a very con- 

 venient reagent, and the only certain one known. 

 A preparation which contains the minimum of free 

 iodine suffices to reveal this substance, though only 

 in case the starch contains water. With an aque- 



1 Nageli: Das Mikroskop, 1877, p. 473. Dippel: Das Mikroskop, 

 1872, p. 273. Sachs : Jahrbiicher fiir wiss. Bot., 1863, III. MohhVer- 

 mischte Schriften, 1845, P- 335- Hofmeister: Handbuch, I, Pflanzenzelle, 

 1867, pp. 252, 387. Weiss: Allgemeine Botanik, 1878, I., pp. 18, 77, 159. 

 Schleiden : Wiegmann's Archiv., 1838, pp. 39, 59. Raspail . Developpement 

 et Analyse microscopique de la Fe'cule. Ann. Sci Nat , i S6r., T. VI., 

 p. 388. Meyen : Untersuchungen iiber den Inhalt der Pflanzenzellen, Ber- 

 lin, 1828, p. 21. Sachs: Lehrbuch der Botanik, 1874, pp 34, 40, 58. 



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