MICROCHEMICAL TESTS 669 



oxalate or carbonate crystals respectively. As the pectate in 

 the middle lamella, it is best recognised by the addition of pure 

 sulphuric acid ; needle-form crystals appear in a few minutes 

 (Molisch). 



Baecker (Mikrokosmos, Stuttgart, xxiii, 1930, p. 126) fixes 

 material in a Ca-free mixture and sections it. If imbedded, care 

 must be taken that the reagents are Ca-free. Tests : (1) Float 

 sections in 3 per cent. H2SO,, under a coverslip ; needles of 

 CaS04 form in a few minutes. (2) Stain five to ten minutes in 

 saturated alcoholic purpurin solution, treat a few minutes in 

 0*75 per cent, (physiologic) salt solution, destain in 70 per cent, 

 alcohol and mount in balsam. Calcified structures, or (if decal- 

 cified) structures formerly containing calcium, are stained an 

 intense rose colour. (3) Treat sections half to one hour in 5 per 

 cent, aqueous solution of AgNOg in bright light ; wash in 

 distilled water and treat one to two minutes with | to 1 per cent, 

 aqueous pyrogallol and then fix five minutes in 5 per cent, sodium 

 thiosulphate. Calcified areas appear black. 



1343. Magnesium. Schimper {Flora, 1890, p. 214) recommends 

 the addition of a solution of sodium phosphate or of microcosmic 

 salt (NaNH4HP04) reduced with a little ammonium chloride. 

 Rhombic crystals of ammonio-magnesiun. phosphate (MgNH4P04) 

 are formed. See also Klein, Oesterr. Bot. Zeits., Ixvi, 1927, p. 15. 



1344. Iron. See § 674. 



1345. Phosphorus. See Angeli, Riv. Biol., x, 1928, p. 702. 



ORGANIC 



1346. Fats. These are treated fully in Chapter XXVIII. 

 page 278, to which refer. 



Fats are immiscible with water and have a different refractive 

 index ; their microscopic appearance in aqueous mounts is 

 therefore characteristic. They are soluble in ether, chloroform, 

 benzene, etc. Fats are fairly rapidly turned brown and then 

 black by 1 per cent, osmic acid solution, but osmic acid also stains 

 proteins brown. Moreover, saturated fats and fatty acids some- 

 times do not reduce osmic acid. They are stained by alkannin, 

 Scharlack R (Hill, New Phyt., xi, 1912, p. 72) and Sudan III, 

 but these and similar reactions are not specific. Ranvier {Tech. 

 Lehrb. Hist., Leipzig, 1888) uses an alcoholic solution of cyanin. 



ZwEiBAUM and Mangenot (C R. Soc. Biol., Ixxxix, 1923, 

 p. 540) find that indophenol blue obtained in nascent state by a 

 mixture of a-naphthol and dimethyl-paraphenylene-diamene (the 

 " nadi " mixture) is a good vital stain for fatty substances. Fats 

 stain a deep blue, essential oils a violet-rose, suberin and cutin 

 a deep violet and lignin a very pale blue. 



Saponification of fats under the microscope was first carried out by 

 Mofisch {Grundriss einer Histochemie der planzlichen Genussmittel Jena, 



