ROOT DISEASES AND INJURIES 73 



leaves, early fall of leaves in autumn, death of certain entire 

 branches, stag-head, and lichens on the bark. When such 

 general symptoms of decline occur without apparent associa- 

 tion with a cause in the branches, leaves or atmospheric con- 

 ditions, the presence of a root trouble may be suspected. V 



Drying and Drowning 

 Caused by too little and too much water in the soil 



Trees must obtain at all times enormous quantities of water 

 from the soil, during the period when, the leaves are expanded. 

 With a normal water supply and a healthy root system, a tree 

 is naturally so balanced in its development of roots and leaf- 

 sm-face, that it is able to supply the water lost in transpiration 

 from the leaves, except under the most abnormal atmospheric 

 conditions. But if the supply of water is limited because the 

 natural rainfall does not soak into the soil, the leaves may tran- 

 spire more water than the roots can take up in a given length of 

 time. This condition will cause sun-scorch of the leaves and' 

 if repeated year after year may cause the death of the tree (see 

 page 22). 



The other extreme of too much water in the soil may result 

 in more speedy death of the tree. The tips of the roots, which 

 are in contact with the soil-particles and absorb water and food 

 materials, must at the same time obtain a ready supply of au- 

 to make healthy growth and perform their function of absorp- 

 tion. The older parts of the roots must also have access to a 

 supply of air in order that the living tissues they contain may 

 function in growth and transporting food materials and water 

 to the parts above ground. If the amount of water in the soil 

 is excessive, it drives out the air, thus disturbing the balance of 

 air and water necessary to plant growth. This results in slow 

 or rapid death of the roots by drowning. The leaves may show 

 sun-scorch injury the same as when too little water is present. 



