SYNTHESIS OF FOOD WITHOUT LIGHT 



153 



While the synthesis of nitrogenous foods presumably can 

 take place in any living cell there are reasons for believing that 

 most of this work is done in the leaf. Mature leaves at the 

 height of their activity contain large amounts of the amide as- 

 paragin that hardly can be accounted for except by the theory 

 that they are manufactured there. Although there is more 

 asparagin present in leaves in the evening than in the morning 

 this does not necessarily imply that light is required for its pro- 

 duction, for both asparagin 

 and carbohydrates would 

 diffuse out of the leaf during 

 the night, and the produc- 

 tion of asparagin could not 

 be kept up for lack of carbo- 

 hydrates which are needed 

 in its manufacture, and 

 which we know can only be 

 made in the light. 



Although approximately 

 four-fifths of the atmos- 

 phere is nitrogen the vast 

 majority of plants are un- 

 able to use it in its un- 

 combined form for food construction, and for this purpose it 

 must be taken, in the case of green plants, mostly in the form 

 of some nitrate, such as calcium or potassium nitrate. The 

 case is different with saprophytic plants, such as the toadstools 

 and their kind, moulds, and many forms of bacteria, for these 

 plants can appropriate for food various nitrogen compounds 

 in the excreta and dead bodies of other plants and animals. 

 Parasitic plants, such as the rusts, mildews, blights and smuts, 

 and those of higher order, such as Cuscuta, appropriate the food 

 of the plants upon which they are parasitic. 



Although the green plants and plants in general are unable 

 to appropriate the free nitrogen of the air, there are a few forms 

 of bacteria which have this power, such as Clostridium Pasteur- 



FIG. 86. Cross section, A, and surface 

 view, B, of a leaf of common moss, showing 

 chloroplasts, c. 



