174 PHYSIOLOGY *0F NUTRITION 



plants that are subjected to illumination. Respiration in plants is connected 

 with protein decomposition, and asparagin is formed as one of the main ni- 

 trogenous products. This process is to be considered as strictly analogous to the 

 formation of urea in animals, but urea is eliminated from the animal body while 

 asparagin is again utilized in the plant body, by means of the energy of sunlight. 

 Pfeffer 1 has demonstrated by microchemical observation, that asparagin dis- 

 appears as carbohydrates accumulate during the process of photosynthesis 

 in sunlight, being used in protein synthesis. When seeds germinate in the 

 dark, however, protein decomposition predominates, and asparagin therefore 

 accumulates. Under usual conditions the synthesis and decomposition of 

 proteins occur simultaneously, but it should be mentioned that the influence 

 of light becomes apparent only in the later stages of germination. In the 

 earlier stages asparagin accumulates, in light as well as in darkness. After- 

 wards asparagin increases in amount only in darkened plants, while lighted 

 plants gradually lose all the asparagin that has previously been formed. These 

 relations were long ago pointed out by Boussingault and were later verified by 

 Meunier. 2 The following table shows some of Meunier's results with phaseolus 

 coccineus. The numbers denote the relative amounts of asparagin found in 

 plants of three different ages, in darkness and in light. 



Relative Amounts of Asparagin in Plants Grown in 

 Age of Plants Darkness Light 



days 



13 1. 13 1. 18 



18 2.28 2.25 



38 5.18 1. 41 



Of the seedlings eighteen days old, those in light contained as much asparagin 

 as those in darkness. In the oldest seedlings, however, the asparagin content 

 had markedly increased in the darkened plants but had decreased in the illumin- 

 ated ones. 



Pfeffer has confined his researches upon asparagin exclusively to the legumes, 

 which are rich in this substance, but Borodin 3 showed that asparagin is very 

 widely distributed and is probably present in the majority of plants. Under the 

 usual conditions of plant life the detection of asparagin is frequently either very 

 difficult or even impossible, but if the plants to be studied are placed in water 

 culture in darkness for several days, then the carbohydrates necessary for pro- 

 tein formation become entirely used up and asparagin accumulates, as Borodin 

 was able to show by microchemical tests. Along with asparagin, Borodin also 

 found tyrosin and leucin. 



1 Pfeffer, W., Untersuchungen iiber die Proteinkorper und die Bedeutung des Asparagins beim Keimen 

 der Samen. Jahrb. wiss. Bot. 8: 429-574. 1872. 



2 Meunier, Fernand, Etude sur l'asparagine. Ann. agron. 6: 275-281. 1880. 



3 Borodin, J., Ueber die physiologische Rolle und die Verbreitung des Asparagins im Pflanzenreiche 

 Bot. Zeitg. 36: 801-832. 1878. 



