iv] MODES OF NUTRITION 97 



to form starch, a synthesis which cannot be carried 

 out in the laboratory by any agency available to 

 chemists apart from the activity of the living cell. 

 The latter effects the combination by making use of 

 the energy of sunlight, and it appears that a very 

 small proportion of the total light falling on the sur- 

 face of the plant may be sufficient for this purpose, 

 nevertheless this fraction is quite essential. In spite 

 of the most careful and protracted investigation the 

 details of this process of the photo-synthesis of starch 

 are imperfectly known ; but carbohydrate in the form 

 of starch is elaborated by the plant organism from 

 inorganic material, and is immediately converted into 

 soluble sugar which is the carbohydrate food of the 

 plant. 



The simple compounds of nitric acid and ammonia 

 are taken into the tissues of the plant and are then 

 combined with the carbohydrate to form amino-acids, 

 and these food-stuffs are further elaborated into the 

 form of proteid. The sugars and proteids pass into 

 circulation in the vascular tissues of the plant and 

 are assimilated by the cells either stored up in the 

 form of proteid, oils, or starch, or oxidised to supply 

 energy. 



We can exhibit this contrast between the nutritive 

 processes of the plant and animal organism as 

 follows. 



