ABSORPTION OF WATER. 57 



time still contain 0*1 per cent, of the salt in question, or a 

 lower or a higher percentage ? De Saussure was the first to 

 attempt an answer. He employed various substances with 

 which he made aqueous solutions containing about I per cent, 

 of the substance, and he found, by quantitative analysis of the 

 unabsorbed residue of the solution, that the water had been 

 absorbed by the plant in much larger proportion than the 

 substance dissolved in it. 



These are some of his results : 



Polygonum Persicaria Bidens cannabina 

 for every 50 parts Of water, absorbed absorbed 



Chloride of Potassium, 147 parts 16*0 parts 



Sodium, 13-0 15-0 



Ammonium, 12*0 17*0 



Sulphate of Copper, 47-0 48*0 



Cane Sugar, 29*0 32*0 



instead of 50 parts of the substance dissolved. 



From these results de Saussure concluded that the roots of 

 plants absorb substances in solution in smaller proportion 

 than the water in which they are dissolved, a conclusion 

 which is known as de Saussure's law. Wolf and others, in 

 repeating de Saussure's experiments, used much more dilute 

 solutions, and found that under these conditions the amount 

 of substance absorbed was larger in proportion than that of 

 water. 



Wolf obtained, for instance, the following results with Phaseolus 

 multiflorus : 



Nitrate of potassium, 



?j 

 

 j> 

 )> 



hence the strength of the solutions actually absorbed in these cases is 

 0-174 per cent., giving a difference of -0-076 per cent. 

 0-109 +0-009 



o* 108 n +0-033 



0*114 ,+ 0-064 



0-030 +0-005 



