88 THE SYNTHESIS OF PROTEINS 



nitrite on the contact inevitable after expression ; thus if tan- 

 nins be present they and the nitrite would interact so that 

 no reaction for nitrite would be given on testing. Also a 

 mechanism may occur in some plants, e.g. Allium, which 

 prevents the detection of nitrite added to the plant juice. 



The sap must be examined immediately after expression ; 

 a plant juice, e.g. Sambucus, may give a positive reaction 

 when first extracted, but a negative reaction after the lapse 

 of a few hours. 



There is, however, no doubt that free nitrites are of com- 

 mon occurrence in the green plant. Aso * established their 

 occurrence in etiolated potato shoots, and Klein f detected 

 them in Erythrina and other plants, but he points out that in 

 some plants, more especially those with root tubercles, the 

 presence of nitrite may be due to the activity of bacteria. 

 Taking such precautions as are indicated above, Anderson 

 found that more than 20 per cent, of the angiosperms of di- 

 verse affinity J examined, gave positive reactions for nitrite. 



It is sometimes assumed that nitrites are toxic to the plant, 

 and that they must be quickly elaborated in a healthy plant 

 and not allowed to accumulate. From culture experiments, 

 it would appear that nitrite is poisonous if supplied to the 

 plant above a certain limit, but this limit apparently varies 

 with the conditions of the habitat of the plant. Feher and 

 Vagi § found that no ill -effect followed when nitrites were 

 added to the soil in amounts up to I gram per kilogram. They 

 later observed that 0-88 per cent, of nitrite, calculated as N 2 3< 

 in clay and sandy soils, and -95 to i-oi per cent, in garden 

 soils rich in humus poisoned the plant. When grown in 

 water culture a greater amount of nitrite is tolerated ; 1-25 to 

 373 per cent, was found to be injurious to growth but not 

 so far as to cause death. 



* Aso : " Beih. Bot. Zentr.," 1903, 15, 20S ; 1914, 32, 146. 



f Klein : id., 30, 141. 



X Aroideae, Caryophyllaceae, Compositae, Cucurbitaccne, Leguminosa\ 

 Lythraceae, Resedaceae, Rosacea?, Salicaceae, Scrophulariaceae, Solanacea-. 

 Ulmaceas and Urticaceae. 



§ Feher and Vagi : " Biochem. Zeit.," 1924, 153, 156 ; 1926, 174, 262. 



