iqiq] CURREXT literature 447 



green, yellow and bright yellow, and finally the oldest ones on the plant are 

 wilting. Meyer points out that this change in color is due to the gradual 

 decomposition of the chlorophylls, while the carotin and xanthophyll remain 

 constant. As this change progresses the chloroplasts become smaller, and in 

 later stages are shriveled granular masses with balls of excreted material about 

 them. With the gradual loss of chlorophyll goes a similar decomposition of 

 the proteins of the chloroplast. It should be mentioned that Meyer adduces 

 evidence for the view that the chloroplast is the main organ for the storage of 

 the proteins manufactured in the foliage leaf, if indeed not the very seat of 

 protein manufacture. The amount of carbohydrates in the leaves also falls 

 with age. Meyer found that when leaves are placed in darkness no reduction 

 occurs in the proteins until the carbohydrates are greatly reduced by respira- 

 tion. The decomposition of the proteins then begins, he believes, as a source 

 of carbon chains for respiration. He states that there is no loss of nitrogen 

 from the leaf during this change, but that the nitrogen residue remains in the 

 leaf, while the carbon chain of the protein is used for respiration. He appar- 

 ently gives the following interpretation of the process: As the leaves become 

 older they become weakened; in this weakened condition the photosynthetic 

 power falls; this leads to a great reduction in the amount of carbohydrates 

 in the leaf, and finally to the decomposition of the proteins of the chloroplasts 

 as a carbon source for respiration; this decomposition of the proteins is 

 accompanied by the decomposition of the chlorophyll and the change in color. 



Schertz, in an unpublished work from this laboratory, finds in many 

 respects parallel behavior in Coleus Blumei. He finds that shortage of nitrates 

 leads to the decomposition of the chlorophyll, and that old leaves can be 

 maintained green by addition of nitrogen fertilizer. He also finds the phos- 

 pholipine content of the leaf greatly reduced as yellowing progresses. His 

 evidence seems good that shortage of nitrogen initiates all of the decomposition 

 of nitrogen compounds (chlorophyll, phospholipines, and proteins), and that it 

 must be looked at as the immediate cause of the loss of chlorophyll. Plants 

 grown in pots are likely to become pot bound and limited in their supply of soil 

 nutrients. 



There are many incompletely worked phases in Meyer's paper; he has 

 filled in some gaps by drawing data from other workers on very different 

 materials; and his work leaves much to be desired in quantitative determina- 

 tions and cultural experiments. All these leave interpretation to bridge broad 

 chasms, and it is therefore not strange if he has missed the initiating cause of 

 loss of chlorophyll. 



If Schertz is right, that the decomposition of chlorophyll in Coleiis Blumei 

 is due to shortage of nitrogen as a building material, it is also conceivable that 

 a great excess of nitrogen may sometimes lead to the decomposition of chloro- 

 phyll due to the dearth of carbon chains produced by the excess of nitrogen. 

 Shortage of magnesium as a building material may sometimes act in a similar 

 way. — Wm. Crocker. 



