THE WATER SUPPLY OF DESERT PLANTS 



Table i 

 Virgin Eucalyptus forest 



201 



The data were kindly provided by Mr. Loneragan of the Forest Depart- 

 ment. The measurements were made in the Eucalyptus astritigens, E. 

 redunca, E. maroitiata and E. diversicolor forest zones. In this winter rain 

 region, the same rules seem to hold : The amount of the surface of the 

 transpiring leaves (equal to the average leaf litter) decreases proportionally 

 with the rainfall, therefore the water supply does not change essentially. 

 There are some deviations from the given proportions, but this can be 

 expected from a relatively short average of 3-6 years. 



The decrease in rainfall and consequent reduction in plant cover density 

 in arid regions creates a greater distance between individual plants and 

 causes the water penetration into the soil to become shallower. Therefore 

 the root systems of plants in arid regions are shallower but the root itself 

 has a greater horizontal growth. 



The shoot/root growth ratio also decreases with the rainfall. Some 

 physiological experiments allow the supposition, that the growth of the 

 shoot is more reduced than the growth of the roots, as the water supply of 

 the plants becomes more critical. Let us consider the growth of pea seedlings 

 in sugar solutions of different concentrations and in an atmosphere with a 

 relative humidity equal to the corresponding sugar solution. The osmotic 



