732 BIOLOGICAL EFFECTS OF RADIATION 



EFFECT OF DARKNESS ON COMPOSITION 



Plants developed in darkness tend to be higher in percentage moisture 

 and in soluble nitrogen and carbohydrates than plants developed in the 

 light. MacDougal (65) found that the percentage moisture in the tops 

 and corms of Arisaema was greater in etiolated plants than in normal 

 ones, and greater in plants with two seasons' growth in darkness than in 

 those with one season's growth without light. The proportion of ash to 

 other dried materials was higher in the etiolated plants. Lubimenko 

 and Karisnev (63) found the tops of wheat seedlings developed in dark- 

 ness to have 4.62 per cent soluble carbohydrates, while those in the 

 light had 2.87 per cent. Soluble carbohydrates were also higher in the 

 residual seed of the etiolated seedlings than in those developed in 

 light. 



Schulz and Thompson (92) made chemical analysis of barberry shoots 

 grown in light-tight boxes placed over field plants. Moisture, starch, 

 reducing sugar, sucrose, water-soluble nitrogen, and ash content, based 

 on percentage of dry weight, were higher in the etiolated shoots than in 

 normal ones. Fats, as determined by ether extract, and hemicellulose 

 were the only substances determined which were approximately the 

 same in both green and etiolated plants. No difference could be deter- 

 mined in the composition of the roots, nor was the stored material 

 appreciably reduced, even though considerable quantities of etiolated 

 sprouts developed. The old tops were removed from all plants used in 

 this test, and apparently the test did not run sufficiently long for the 

 new green tops to begin storing materials in the roots. The higher 

 percentage of solutes in the dry material of etiolated sprouts is a result, 

 in part, of the lower content of insoluble carbohydrates. 



The ability of plants to use nitrates in darkness to form asparagin 

 was demonstrated by Suzuki (104) who used potato shoots detached from 

 the tuber and cultivated in sugar solution. Tokarewa (108) analyzed 

 etiolated lupine seedlings for nitrogen content. Substantial quantities 

 of asparagin and small amounts of creatinin and betaine were found. 

 Plants containing a considerable amount of asparagin had no carnosin. 

 Asparagin has also been found in etiolated soy bean seedlings by Schulze 

 (91) and in etiolated maize seedlings by Jodidi (53). Jodidi (52, 53) 

 studied the chemical composition of etiolated corn seedlings during the 

 first few days following germination and also the composition of the 

 ungerminated seed. Proteins were rapidly used up by the seedlings so 

 that after 8 days as much as 48 per cent of them were converted into 

 soluble nitrogen compounds. From the second to the eighth day the 

 distribution of nitrogen in the aqueous extract changed as follows: (a) 

 Amide nitrogen increased from 11.44 to 18.08 per cent. (6) Humin 

 nitrogen decreased from 19.51 to 6.45 per cent, (c) Amino nitrogen 



