CHAPTER IV 



THE PRESENCE OF INORGANIC IRON COMPOUNDS IN THE 

 CHLOROPLASTS OF THE GREEN CELLS OF PLANTS, 

 CONSIDERED IN RELATIONSHIP TO NATURAL PHOTO- 

 SYNTHESIS AND THE ORIGIN OF LIFE 



SINCE the days of de Saussure, 1 now over a century ago, the green 

 colouring matter of the leaf, chlorophyll, has been regarded as the 

 fundamental agent for the worldwide photo- synthesis of living 

 matter. But it is remarkable how completely this view is based 

 upon indirect or circumstantial evidence, and how little, if any, 

 direct observation can be cited in its support. 



Chlorophyll is known by the biochemist to be one of the most 

 complex of substances, comparable to haemoglobin in its molecular 

 structure, and yielding a host of disintegration constituents them- 

 selves complicated substances of high molecular weight. Between 

 the simple colloidal molecules of inorganic iron salts in solution or 

 suspension and such a highly complex organic substance as chloro- 

 phyll there is a wide interval, and it was with the view of dis- 

 covering some intermediate links or finding some explanation for 

 the gap that the present experiments were commenced. 



Before describing the experiments in detail it is desirable to 

 touch upon present views as to photo- synthesis in the green cell as 

 far as these bear upon our investigation, in order to give an appro- 

 priate setting to the new facts, and show how present knowledge 

 regarding the absolute necessity for the presence of iron in the green 

 leaf, which has been hitherto devoid of all explanation, led up to 

 these experiments. 



Photo- synthesis with production of oxygen only occurs in the 

 chlorophyll- containing parts of the plant, and only in these when 

 they are exposed to light. Also, when a plant is allowed to grow in 

 darkness, the leaves are found to be pale yellow in colour, or chlorotic, 

 instead of green. When a plant grown in darkness, and, as a result, 

 possessing chlorotic leaves, is then exposed to light, the pale yellow 



" Recherches Chimiques sur la Vegetation" (1804). OstwalcTs Klas- 

 slkzr, No.s. 15 and 16. 



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