J; . CHAPTER X 



THE PHYSIOLOGY OF NUTRITION 



Physiology. That division of botany which investigates 

 the work which plants can perform is called physiology. 

 Physiology shows us how each structure is adapted to the 

 functions which a plant, or organs of a plant, can perform. In 

 simple plants like Protococcus which grows on walls, trunks of 

 trees, and can live if it is only damp, the entire body of the 

 plant consists of a single cell, which performs all the work 

 necessary both for the life of the plant and for the reproduction 

 of its kind. In most multicellular plants, as we have seen, the 

 constituent cells differ very much in structure, and this difference 

 of structure is connected with the performance of some particular 

 function. 



In all the higher plants we obtain what is known as division 

 of labour. Each special part of the plant has some special 

 work to perform. The roots collect water and minerals ; the 

 leaves take in carbon dioxide ; the stem conducts the water 

 from the roots to the leaves ; and the leaves from these materials 

 form sugar, starch, cellulose, and proteids. 



The striking attributes which especially characterise plants as 

 living bodies, and by which they can be distinguished from non- 

 living bodies, are (i) that from time to time food is taken in and 

 the plant grows, (ii) movements are carried out by the plant 

 for its benefit, (iii) certain parts of the plant are separated, and 

 these parts produce new individuals, z.e., reproduction takes 

 place. 



Nutrition. Those processes which go on in a plant and 

 by which it is able to form new material from the constituents 



