6o THE BIOLOGY OF FLOWERING PLANTS 



TABLE XV 

 Relation of Soil Moisture to Water Intake by Xanthium Seeds 



The relation for some other soils at a water content of 

 about the wilting coefficient is given in Table XVI. 



TABLE XVI 



Intake of Water by Xanthium Seeds from Various Soils at Wilting 



Coefficient 



Ursprung and Blum (192 16) observed that the suction force 

 of the root cells became very quickly accommodated to the 

 osmotic pressure of a solution to which they were trans- 

 ferred. Thus bean roots growing in sawdust had a suction 

 force of I "4 atmospheres; transferred to a 0*65 per cent, solu- 

 tion of sugar with osmotic pressure of 5-3 atmospheres, the 

 suction force rose to 5-7 atmospheres in less than four days. 

 These investigators consider, therefore, that the suction 

 force of the root cells, which can be determined as already 



