;6z 



FINE-STRUCTURE OF PROTOPLASM 



IE 



vital staining of living cytoplasm is almost impossible. The enhanced 

 adsorbing power of dead cytoplasm allows of identifying dead cells 

 with the fluorochrome acridin-orange (Strugger, 1949)- Depending 

 on its concentration, this dye shows a green (1:50,000) or a red 

 (1:100) fluorescence in the UV light. Since dead cytoplasm adsorbs 

 a considerable amount of acridin-orange, it displays a magnificent red 

 fluorescence, whereas living cells appear to be green. 



With the aid of the diagram of Fig. 96 (p. 145) some indication 

 of the sio-nificance of the various elements in the structure of the proto- 

 plasm can be given. In the periodic system (Table XX) all elements 

 which are of importance to the life of plants lie on a line connecting 

 carbon with the inert gas argon. I have designated this line as the 

 nutrition line (1935c); only hydrogen and molybdenum (Arnon and 

 Stout, 1939) are an exception. 



TABLE XX 

 elements which are indispensable to plant nutrition 



In Table XX the indispensable elements have been framed by 

 squares, whereas those which are found in nearly all plants, but whose 

 indispensability remains to be proved, have been framed in dotted 

 lines. C and N Ue in the centre. These elements occupy a central 

 position in the molecular structure, too, since they form the poly- 

 peptide main chains. They may therefore be designated as chain- 

 building elements. The chains are built according to the scheme 

 -C-C-N-C-C-N-. Notwithstanding its close relation to nitrogen, 

 phosphorus does not occur as a chain-building element in this manner, 

 but only in combination with oxygen (compare Fig. 122, p. 215: 

 -C-0-P-0-C-) ; as in the inorganic domain, it is always present in 

 an oxidized form as phosphoric acid. In the degradation of carbo- 



