808 THE ROLE OF NITROGEN, ETC., I., 



-embryo. By determining the amount of free acid from day to 

 day, the activity of the lipase may be found. It is possible to 

 activate the zymogen by various mechanical or chemical means, 

 but different methods are necessary with different kinds of seeds. 

 This points to a probable difference in the zymogens. Again, 

 active solutions of lipase can be prepared from germinating seeds, 

 and from these solutions alcohol may precipitate the enzyme 

 completely in some and not at all in others. This suggests that 

 different lipases exist in various seeds. 



Absorption of Nitrogenous Food. 



Liebig considered that ammonia was the chief source of the 

 nitrogen of plants, while Boussingault held that the nitrates of 

 the soil were most essential. It is certain that both are valuable; 

 some plants are found to prefer nitrates, others ammonia, while 

 others again are indifferent. Nitrites, too, are of considerable 

 value, and Treboux(18) states that the value of the amino-acids 

 and amides, is much less, yet these, too. form important sources 

 of nitrogen. For some fungi the food-value of the simple amino- 

 acids is higher than that of all other forms of nitrogen. (19) 



Large amounts of nitrates are found in many plants, such as 

 the sunflower, turnip, potato[l'5to 2-8%], in Amaranthus [15%], 

 in Chenopodium, Urtica, etc.;(20) the nitrates are absorbed by the 

 roots, and when plants are grown in nitrate-free soil none is found 

 in the tissues. We thus see that nitrates can be stored in plants 

 as reserve-material, but nitrites and ammonium salts are poisonous 

 and must be immediately used. 



Now the nitrates and nitrites undergo reduction in green 

 plants, and a reducing enzyme was discovered in potatoes by 

 Abelous and Aloy(21) in 1903, and confirmed in other vegetables 

 by Kastle and Elvolve(22) in 1904. This enzyme has recently 

 been isolated by Irving and Hankinson(23) (1908), who found it 

 in the roots, stems and leaves of Vicia Faba, in the iris, and 

 various graminese. They state that the conditions necessary for 

 nitrate-reduction are the presence of the enzyme and a suitable 

 carbohydrate to supply the necessary energy. There is also 



