CHAPTEE III 



OUTLINES OF THE PHYSIOLOGY OF NUTRITION 



IN studying our first two types we have obtained a 

 general idea of the form and structure of the root and 

 shoot in green plants. We have also learnt some- 

 thing as to their functions. It will be well for us, 

 however, before proceeding further, to endeavour to 

 gain a more connected view of the mode of working of 

 i he vegetative organs. We have to learn what food 

 the plant needs ; from what sources its various kinds 

 of food are obtained ; what changes they have to 

 undergo in order to be made use of by the plant; we 

 have also to inquire how plants breathe ; and gener- 

 ally, what are the actions which a plant carries on as 

 a living organism. All these are physiological questions, 

 for we have already learnt that physiology asks what 

 is the work done by plants and their organs. We 

 shall only attempt here to give a very short and simple 

 answer to these inquiries ; anything like a full answer 

 would require an advanced knowledge of physics and 

 chemistry, which we must not take for granted. A 

 little elementary knowledge of these two subjects is 

 indeed absolutely necessary, if we wish to understand 



even the simplest facts about the life of plants. 



200 



