CHAPTER I 



HISTORICAL INTRODUCTION 



In the year 1699 Woodward published the results of experiments 

 in which cuttings of plants were grown, not in soil, but in rain 

 water. More than a century and a half later Julius Sachs (1860) 

 and W. Knop (1860) independently developed this method of 

 water culture by growing plants of several different species in a 

 dilute aqueous solution of various salts. In this way the materials 

 available for absorption by the roots of the growing plants were 

 controlled, and Sachs and Knop concluded from their experi- 

 ments that so long as the culture solution contained salts in- 

 volving the elements nitrogen, sulphur, phosphorus, potassium, 

 calcium, magnesium and iron, a perfectly healthy plant would 

 result. The elements occur in soil as constituents of compounds 

 present in, or derived from, the minerals of the underlying rock, 

 and are therefore generally known as mineral nutrients. Ex- 

 periments of this kind have been repeatedly carried out by 

 subsequent investigators and many formulae for water-culture 

 solutions have been used and recommended. The water-culture 

 method has also been extensively used for research in plant 

 nutrition. Some of the best known and most widely used water- 

 culture solutions are those of Sachs and Knop themselves and 

 the later ones of Pfeffer and Von der Crone. Plants of a great 

 number of species have been successfully grown in water culture, 

 and in recent years the method has been advocated, perhaps too 

 optimistically (cf. Hoagland and Arnon, 1938), as a means of 

 cultivating certain crop plants on a commercial or semi- 

 commercial scale. The compositions of some of the best known 

 and most widely used water cultures are given below. 



Sachs's nutrient solution 



Potassium nitrate l'Og. 



Sodium chloride 0-5 g. 



Calcium sulphate 0-5 g. 



Magnesium sulphate 0-5 g. 



Calcium phosphate 0-5 g. 



Water 1 1. 



A few drops of a solution of ferric chloride or ferrous sulphate. 



