OF THE GREEN CELLS OF PLANTS 67 



such incrustations of iron oxide on their leaves when grown in water 

 containing only traces of iron, but in such cases it is also found that 

 the chloroplasts of the green cell itself are very rich in inorganic iron. 

 The higher aquatic plants examined have been these two and a 

 variety of watercress, and all three were found to give a strong 

 positive reaction. 



Ordinary lawn grass contains a high percentage of iron in the ash, 

 and, when teased out and deprived of chlorophyll by hot alcohol, 

 forms a very suitable object on account of the ease with which 

 strands of fibre with attached cells separate. The staining of the 

 chloroplasts is at first a dark brown, passing later into a blue-black. 

 The leaves of many species of dicotyledonous plants were examined, 

 and it was found that here the transition from dark brown to blue- 

 black was much slower as a rule, and in some cases the staining 

 remained permanently of a deep orange- brown to a pure dark 

 brown colour. But in all cases the chloroplasts stained more deeply 

 than the remainder of the cytoplasm. 



The catalyst for the photo- synthesis may not in all cases be an 

 iron salt, or oxide, but an iron salt is present and capable of operating 

 as a catalyst in a large number of instances. 



Various substances known to be present in the ash of leaves have 

 been tested for their photo- synthetic activity in connection with the 

 work, and it has been found that magnesium and calcium phosphates 

 and bicarbonates are entirely ineffectual, but that marked photo- 

 synthesis of formaldehyde is obtained with chlorides or colloidal 

 hydrates of iron or aluminium. 



SUMMARY 



1 . Inorganic iron salts and iron or aluminium hydrates in colloidal 

 solution possess the power of transforming the energy of the sunlight 

 into chemical energy of organic compounds. 



2. Inorganic iron, in crystalloidal or colloidal form, is present 

 in the colourless part of the chloroplast of the green plant cell in 

 many plants. 



3. In the absence of iron the green colouring matter cannot 

 develop in the leaf, although the green colouring matter itself 

 contains no iron. 



4. In the presence of sunshine, the iron- containing substance of 

 the chloroplast develops the colouring matter, so that this itself is a 



