CHAPTER VII 

 MATERIAL TRANSFORMATIONS IN THE PLANT^ 



§1. The Cell as the Physiological Unit.^ — All plants are composed of one 

 or more cells, each of which consists essentially of cytoplasm and nucleus. 

 Observations and experiments have shown that the life of the cell depends upon 

 the activities of these two parts and that the other parts of the cell are formed 

 by these. The life of a many-celled plant is thus nothing but the sum 

 total of the lives of its individual cells. For this reason the cell may be charac- 

 terized as the elementary organism.^ We know of no organism with a structure 

 simpler than that of a single cell. 



The nucleus and the cytoplasm both have peculiar internal structures and 

 their chemical nature is very complicated and not well understood. The dried 

 Plasmodium of the slime-mould Mihalium septicum, consisting almost entirely 

 of cytoplasm and nuclei, has the following chemical composition expressed, in 

 percentages of dry weight:* 



Proteins 40 Cholesterin 2.0 



Albumins and enzymes ij Resins. 1.2 



Other nitro-jenous compounds 2 Calcium salts (except CaCOs) 0.5 



Fats 12 Other salts 6.5 



Carbohydrates 12 Undetermined materials 6.5 



The cytoplasm and nucleus thus consist mostly of proteins, very compli- 

 cated nitrogenous compounds, many of which contain phosphorus. After 

 treatment of proteins with gastric juice or trypsin there remains an undissolved 

 residue containing nucleic acid. The nucleus, the cytoplasm, chloroplasts, 

 leucoplasts, and all other living constituents of the cell are only partially dis- 

 solved in gastric juice (exceptions to this statement are very rare) . On the other 

 hand, the simple proteins (constituents of aleurone grains, albumin crystals, 

 etc.), are completely soluble in gastric juice. The amount of simple proteins 

 in cytoplasm and nucleus is so small that it cannot be determined at all by micro- 

 chemical methods, or this is possible only with special precautions. 



' Euler, H., Grvindlagen und Ergebnisse der Pflanzenchemie. 2 v. Braunschweig, 1908-1909. 



2 Verworn, M., Allgemeine Physiologie. S Aufl. Jena, 1909. [Idem, General physiology. Translated 

 by P. S. Lee, from the 2nd Ger. ed. XVI + 599 p. London, 1899.I Reinke, J., Einleitung in die theo- 

 retische Biologie. ;« Aufl. S78 p. Berlin, 191 1. Hofmeister, F., Die chemische Organisation der Zelle. 

 Braunschweig, 1901. [HBber, 1914. (See note i, p. no.)] 



" Bittcke, Ernst, Die Elementarorganismen. Sitzungsber. (math.-naturw. Kl.) K. Akad. Wiss. Wiea 14^ : 

 381-406. 1861. 



' Reinke, 1881. [See note i, p. 30.I 



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