Robert B. Withrow 401 



may explain, in part at least, observations that magnesium and phos- 

 phorus are frequently taken up at parallel rates in higher plants. 



Iron has long been recognized as an essential micronutrient for the 

 synthesis of chlorophyll. Jacobson (25) determined the iron content of 

 pear, tobacco, and corn leaves in relation to varying degrees of iron 

 chlorosis. He found that both total iron and acid-soluble iron paralleled 

 the chlorophyll content, but he found also that some of the iron is inac- 

 tive in chlorophyll synthesis and this must be exceeded before chloro- 

 phyll formation can proceed. He observed that the "active" or ferrous 

 iron was localized chiefly in the chloroplasts. This is in harmony with 

 the idea advanced by Mommaerts (36) that chlorophyll in the leaf exists 

 in combination with a protein and that such a chlorophyll-protein com- 

 plex contains iron. In addition iron-containing compounds of this type 

 have been isolated from corn and tobacco. It has been suggested that the 

 iron is associated closely with a protein and that this protein complex, 

 which apparently catalyzes chlorophyll formation, serves as a "chloro- 

 phyll enzyme." 



Neish (40) has found that there is a greater percentage of copper in 

 the chloroplasts than in the remainder of the leaf. In Birfolium pratens, 

 the proportion was 74.6 per cent of the total. It has been found in some 

 plants that there is a greater concentration and longer persistence of 

 chlorophyll in copper-treated plants. Working with a variety of plants, 

 Okunsov (43) found a marked increase in chlorophyll content of the 

 leaves on the addition of copper sulfate spray when the plants were 

 grown on a copper-deficient turf. The increased chlorophyll was held 

 as principally due to a retarding effect of copper on the decomposition 

 of chlorophyll with age. Arnon (/) has shown copper to be a com- 

 ponent of the chloroplast of chard as a polyphenol oxidase. This is a 

 copper-protein complex which may play a role in the evolution of 

 oxygen by isolated chloroplasts during the water-splitting phase of 

 photosynthesis. 



PHOTOSYNTHESIS 



Current interpretation of photosynthesis as an over-all process is tend- 

 ing increasingly toward the view that the reduction of carbon dioxide 

 and the fission of water with the evolution of oxygen is a relatively 



