Lecture 2. 



MICRONUTRIENT CHEMICAL ELEMENTS 

 AND PLANT GROWTH 



For about three quarters of a century the assump- 

 tion was a general one by botanists and workers in the 

 field of agricultural investigation that only ten chem- 

 ical elements were universally indispensable for the 

 growth of higher green plants ; namely, carbon, hydro- 

 gen, oxygen, nitrogen, sulphur, potassium, calcium, 

 magnesium, phosphorus and iron. The last seven 

 were considered to be the essential elements of the 

 nutrient medium. It was early recognized, of course, 

 that many other chemical elements might be found in 

 plant tissues, but this fact, while it gave a basis for 

 certain presumptions, could not establish the essential- 

 ity of the elements present. Some investigators also 

 observed that minute amounts of certain chemical 

 elements added to the culture medium produced at 

 times beneficial effects on plant growth. These were 

 often regarded as "stimulating" effects. It was sup- 

 posed that elements of a toxic nature could stimulate 

 plant growth when present in extreme dilution. 



Maze in France (1914), following observations by 

 other French workers, reported an investigation under- 

 taken from a different point of view. He grew maize 

 plants in highly purified salt solutions and concluded 

 that chemical elements in rather large number were 

 essential for the plant in very minute amounts. Im- 

 portant and fundamental in concept as Maze's experi- 



