SYNTHESIS IN THE PLANT 323 



alcohol, in which prolamins are insoluble, and ether. The 

 ether is added in order to make the precipitation more com- 

 plete and also to hold any fats which may have been ex- 

 tracted by the alcohol. 



THE SYNTHESIS OF PROTEINS IN THE PLANT. 



In view of our limitations as regards the chemistry of pro- 

 teins, it is not surprising that we are in almost complete ignor- 

 ance respecting the synthesis of these substances in plants. 



It is generally agreed that the leaves are the important 

 centres of protein formation, and they show a periodicity in 

 their nitrogen content. Thus Otto and Kooper * and Le Clerc 

 du Sablon f found that there is a gradually decreasing amount 

 of nitrogen from the spring to the autumn, and that leaves of 

 several different plants, even in different stages of development, 

 exhibit a greater nitrogen content in the morning than in the 

 evening. 



The requisite nitrogen is obtained, not from the air — ^the 

 Leguminosae are here excluded — but from the salts contained 

 in the water absorbed by the roots; thus the fertility of soil, 

 especially with regard to nitrates, is most important, as has 

 been shown by direct experiments. :J: 



In passing, it may be remarked that some plants, at any 

 rate, can make use of salts of ammonium as a source of 

 nitrogen. Hutchinson and Miller § found this to be true under 

 conditions of culture which precluded the presence of nitrates 

 in the soil. In this respect, however, all plants do not behave 

 alike ; whilst some will grow equally well whether supplied 

 with nitrates or ammonium salts, others flourish best when 

 supplied with the former, and others seemingly prefer am- 

 monium salts to begin with and then nitrates. 



Since protein formation takes place particularly in the 

 leaves, it might be supposed that light is an important and di- 

 rect factor in its synthesis. Indeed earlier workers, Schim- 

 per II for example, considered this to be so, but more recent 

 investigations tend to show that the synthesis of proteins 



*Otto and Kooper: " Landwirthsch. Jahrb.," igro, 39. 

 t Le Clerc du Sablon : " Rev. Gen. Bot.," 1904, 16, 341. 

 tWhitson and Stoddart: "Ann. Rep. Wisconsin Exp. Sta.," 1904, 193. 

 §Hutchinson and Miller: "Journ. Agric. Sci.," igog, 3, 179. 

 I| Schimper; "Flora," 1890, 73, 207. 

 21 * 



