202 



H.WALTER 



pressure of the cell-sap and therefore also the hydrature of the protoplasm, 

 is in this case nearly equal to the osmotic pressure of the sugar solution. 

 The results show that with increasing osmotic pressure from o to 30 atm 

 (i.e. decreasing hydrature from 100-98%), the growth of the shoot decreases 

 rapidly reaching zero at about 20 atm, but on the contrary to this, the 

 growth of the root first increases three times, reaching a maximum at 7 

 atm( = 99-5% hy) and only then decreases . It was still measurable however, 

 at 30 atm (Fig. 3). Kausch (1955) mentioned that the same is true if the 



eooo 

 Kglha 



iOOO 



mo 



JOM 



2000 



1000 



m 



200 



JSO 



■wo 



500 mm 600 



Fig. 2. The productivity of grassland (kg/ha) in relation to the mean yearly rainfall 



in mm (from H. Walter, 1954). 



soil moisture decreases. The behaviour of side roots is different and similar 

 to that of the shoot. 



Under humid conditions the osmotic pressure is low, therefore we have 

 to expect a vigorous shoot and side root growth, but slow growth of the 

 main root. With increasing aridity the osmotic pressure increases, the 

 growth of the shoot is retarded, also that of side roots, but elongation oi 

 main root is increased. This is in accordance with the facts observed in the 

 field : the shoot/root ratio of plants in arid regions decreases with the 

 rainfall. Simonis (1936) grew TrifoUum incarnatmn in moist soil (80% of 



