CHAPTER II. — SPECIAL PHYSIOLOGY OF THE NUTRITIVE FUNCTIONS. 715 



4 3 12 5 



Fio. 471.— Water-cultures of Buckwheat (after Nobbe). 



No. 1. Plant grown in normal solution. 



without potassium. 



with sodium-salts instead of potassium. 



without calcium. 



without nitrates or salts of ammonia. 



This method of experimental culture, which is known as water- 

 culture, has been of the greatest service in determining which are 



