2 EXPERIMENTAL PLANT PHYSIOLOGY 



The following is a list of the more common salts 

 dissolved in the water of the soil : 



Common table salt, made up of sodium and chlorine. 

 Gypsum „ ,, calcium, sulphur, and 



oxygen. 

 Epsom salts „ „ magnesium, sulphur, 



and oxygen. 

 Glauber's salts ,, „ sodium, sulphur, and 



Traces of chlorides, ' 

 nitrates, and phos- 

 phates of calcium, 

 magnesium, and 

 potassium 



oxygen, 

 'chlorme, nitrogen, 

 oxygen, phosphorus, 

 calcmm, magnesium, 

 and potassium. 



From this list it appears that the substances present 

 (called by the chemist "elements") are: sodium, 

 chlorine, calcium, magnesium, sulphur, oxygen, nitro- 

 gen, phosphorus, and potassium. 



It must be remembered that these are the more 

 common elements present in solution in the soil, but 

 they are not the only ones that may be present ; for 

 instance, the important element, carbon, is often there. 

 It is a compound of carbon, calcium bi-carbonate, that 

 causes the " hardness " of water in limestone districts. 

 But, as it will be shown later, carbon compounds in the 

 soil are not necessary for plant-life. A plant thrives 

 just as well in a soil that contains no carbon as in one 

 in which this element is present. 



In the soil, then, certain substances are present that 

 are available as food. By a series of simple experiments 

 it is possible to find out how far these substances are 

 made use of in the feeding-processes of the plant. 



11. THE ABSORPTION OF POOD PROM THE SOIL 



In the working of any experiment there are four 

 distinct steps that have to be considered. In the first 

 place it is necessary to formulate a definite aim. After 



