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PHYSIOLOGY OF NUTRITION 



Time of Analysis 



Total 

 Ash Content 



Absolute Amount of 

 Potassium 



May 



June 



July 



August. . . . 

 October. . . 

 November 



grams 

 0.7 

 1 . 2 

 1 . 2 

 1 . 1 

 0.8 

 0.7 



The percentage content of potassium in the ash underwent a marked decrease 

 during the course of the summer, but no corresponding decrease in the absolute 

 amount of potassium is apparent. The absolute amount is maintained fairly- 

 constant during the growing period, and undergoes a marked decrease only 

 in late autumn. Similar results were also obtained for phosphoric acid (PO4). 

 §5. Microchemical Ash-analysis. °— Ash-analyses of the kind just referred 

 to can be carried out only with large amounts of material, but in exact studies 

 of the distribution and translocation of ash-constituents small quantities must 

 suffice, and microchemical analysis is resorted to in such cases. 1 Platinic 

 chloride is used for the identification of potassium, beautiful crystals of potas- 

 sium chloroplatinate being formed (Fig. 52). To identify calcium, dilute sul- 



1 Haushofer, K., Mikroskopische Reaktionen. Braunschweig, 1885. Klement, Constantin, and Renard, 

 A., Reactions microchimiques a cristaux et leur application en analyse qualitative. 132 p. Bruxelles,i'i886. 

 Schimper, A. F. W., Zur Frage der Assimilation der Mineralsalze durch die griine Pflanze. Flora 73 :'207- 

 261. 1800. P. 207. [Zimmerman, A., Die botanischen Mikrotechnik. Tubingen, 1892. Idem., 

 Botanical microtechnique, a handbook of methods for the preparation, staining, and microscopical 

 investigation of vegetable structures. Translated by J. E. Humphrey. XII + 296 p. New York, 1893. 

 Richter, O., Die Fortschritte der botanischen Mikrochemie seit Zimmermann's Botanische Mikrotechnik. 

 Sammelreferat Zeitsch. wiss. Mikroskopie 22: 194-261. 1905. Emich, F., Lehrbuch der Mikrochemie. 

 Wiesbaden, 191 1. Molisch, Hans, Mikrochemie der Pflanze. Jena, 1913.] 



" On these methods for ash-analysis the reader is referred to Molisch, 1913, cited just 

 below. The following points may be of value in connection with the discussion given in the 

 text. The reaction given for potassium fails to distinguish between potassium and ammonium. 

 (On this difficulty see: Weevers, Th. I., Untersuchungen liber die Lokalization und Funktion 

 des Kaliums in der Pflanze. Recueil trav. bot. neerland. 8: 289. 191 1.) When calcium 

 is plentiful the crystals mentioned occur in dense masses, so that their individual form is seen 

 only at the periphery of the mass. The reaction here given for iron serves only to identify it 

 when in the ferrous condition. For other tests for this element in inorganic compounds see 

 Molisch, 1913. In organic compounds {masked iron) it cannot be identified by any known 

 microchemical methods. (See: Wiener, Adele, Microchemical proof of iron, especially 

 masked, in plants. Rev. in: Chem. abstracts 11: 615-616. 1917. [Original not seen; 

 cited as: Biochem. Zeitsch. 77: 27-50. 1916.].) To identify phosphorus in organic com- 

 pounds it is necessary first to incinerate the material, after which the test given may be applied. 

 The precipitation of the phosphate ion as ammonium-magnesium phosphate (see under 

 magnesium) offers a more sensitive method, not affected by the presence of organic substances. 

 (See Molisch, 1913.) The tests for sulphur given in the text apply only to sulphates and 

 are, moreover, not reliable for plant tissues. There is no microchemical test available for 

 sulphur as it is usually encountered in plant cells. A more reliable test for chlorides is that 

 of Macallum. (See: Macallum, A. B., On the nature of the silver reaction in animal and 

 vegetable tissues. Proc. Roy. Soc, London B 76: 217-229. 1905.) — Ed. 



