2 MINERAL SALTS ABSORPTION IN PLANTS 



basis of these observations, he disputed Van Helmont's conclusion, 

 and asserted that "earth, and not water, is the matter that constitutes 

 vegetables." 



Although Hales (Vegetable Staticks, 1727) perceived that plants 

 are nourished in part from the air through the leaves, it was not until 

 the nineteenth century that a proper distinction was made between 

 photosynthesis and mineral nutrition. De Saussure (Recherches 

 chimiques sur la Vegetation, 1804) maintained that the soil supplies a 

 small but essential part of plant nutrients, including nitrogen and 



Table 1, 



Growth of Mint Plants in Water from 

 Various Sources 

 (Woodward, 1699) 



mineral elements. He showed that if a plant is grown from seed in 

 water alone, there is no gain in ash except for the relatively small 

 increment which may result from deposition of dust. In spite of his 

 clear experimental results and logical arguments, De Saussure's 

 ideas did not receive immediate acceptance, nor were his quantitative 

 methods of investigation adopted generally until more than 50 years 

 later. The view that inorganic substances are mere accidental 

 inclusions in plants, or at best mysterious "stimulants" rather than 

 nutrients, was finally discarded following trenchant criticism by 

 the chemist Liebig, in a famous address to the British Association 

 for the Advancement of Science {Die organische Chemie in ihrer 

 Amvendung auf Agricultur imd Physiologie, 1840). The difficult 

 problem of the sources of nitrogen for plants gave rise to much 

 discussion towards the middle of the last century. Liebig maintained 

 that gaseous nitrogen is not utilized and that the element is probably 

 obtained by plants as ammonia from its surroundings. In 1856, he 

 showed that nitrate is formed from nitrogenous fertilizers in soil, 



