THE CARBOHYDRATES OF THE ANGIOSPERM LEAF 19 



weight, M, of the sap solutes. This shows that the total 

 osmotic pressure can only be due in part to sucrose, though 

 it is the only sugar present normally in the mature root in 

 any considerable quantity. 



These measurements were made without previous 

 treatment of the roots with liquid air. Accordingly they 

 are somewhat too low, as previously pointed out. Inspec- 

 tion of Table 9 makes this point clear. In it is also recorded 

 the electrical conductivity of the sap, expressed as recipro- 

 cals of the conductivity in ohms. Under A e is given the 

 depression of freezing-point occasioned by the electrolytes ; 

 this is calculated from the conductivity C, as explained in 

 a subsequent chapter. A - A e therefore represents very 

 approximately the depression produced by the non- 

 electrolytes, which consist almost exclusively of sucrose in 



this case. 



TABLE IX. 



Since a 1 per cent, solution of sucrose* lowers the 

 freezing-point of water 0-054, it may be seen that a 

 depression of 1-484 due to non-electrolytes points to the 

 existence of slightly over 27 per cent, of sucrose in the sap. 

 The difference of under 3 per cent, in the electrical con- 

 ductivity in favour of the untreated tissue may be put 

 down to a local difference, or it may be partly due to the 



* The depression produced by a 1 per cent, solution of glucose or 

 fructose amounts to 0-106. 



