CHAPTER L 

 MICROCHEMICAL TESTS 



1337. In this chapter are given some tests for microchemical 

 substances as applied to plants. Additional information will be 

 found in Chapter XLVII and Chapters XXVII, XXVIII and 

 XXIX. 



INORGANIC 



Studies of the distribution of soluble, diffusible salts are best 

 made on sections prepared by a freezing method. See § 1340. 



1338. Sulphur may be found in the free state as globules on or 

 in filaments of algse, bacteria and fungi growing in sulphurous 

 water. The globules are soluble in CSg if the plants are first killed 

 by drying or otherwise. See also Klein, Oesterr. Bot. Zeits., Ixvi, 

 1927, p. 15. 



1339. Silica is best recognised after incineration of sections, the 

 siliceous portions remaining comparatively unaltered. It is 

 soluble in HF. For silica in the cell- wall, Molisch treats sections 

 on a slide, coated with varnish or Canada balsam, with aqua regia 

 or Schultze's reagent, washes with water and then tests with HF. 

 See also Brown, Bull. Torrey Bot. Club, xlvii, 1920, p. 407. 



1340. Potassium. Macallum [Journ. Physiol., xxxii, 1905, 

 p. 95) uses the hexanitrate of Co and Na, which in the presence 

 of sodium acetate gives an immediate precipitate for potassium. 

 The precipitate is rendered more visible by ammonium sulphide, 

 which makes it densely black. Dowding {Ann. Bot., xxxix, 

 1925, p. 459) freezes the material with solid COg at — 50° C, cuts 

 it frozen and thaws it after it is placed in the reagent. This 

 prevents diffusion. Place sections one to two minutes in the 

 cobalt reagent, wash twenty to thirty minutes in a succession of 

 basins kept over ice-cold water over a freezing bath and mount 

 in glycerine and fresh ammonium sulphide. 



According to Molisch {Microchemie der Pflanzen, Ix, 1921) 

 ammonia gives a similar reaction, but its presence in fresh material 

 is unlikely. Nessler's reagent will test its presence. 



1341. Sodium. Streng {Zeits. Wiss. Mikr., iii, p. 129) recom- 

 mends the use of uranyl-magnesium acetate. Schimper {Flora, 

 1890, p. 207) used uranyl acetate. Molitylin and Tubokario 

 {Microchem., vii, 1929, p. 334) use zinc uranyl acetate. 



1342. Calcium in the cell sap may be recognised by the addition 

 of ammonium oxalate or ammonium carbonate, forming calcium 



668 



