THE DISEASES OF TIMBER TREES. 59 



at the time of lopping branches, are the usual means of prevent- 

 ing the rot from taking place. 1 



(2) Diseases due to the Influence of the Soil. 

 Stay-headedness, or decay of the summit of the crown, may be 

 the consequence of want of nourishment and moisture, or also due 

 to old age. In high forests of Beech it may be noted long before 

 the trees are mature, when the removal of the fallen leaves from the 

 soil has been continued for any length of time ; in forests of Oak, 

 in consequence of interruption of the canopy, and consequent 

 deterioration of the soil; in Alder crops, as the result of too 

 thorough drainage ; and on Oak standards also, as the effect of 

 being suddenly admitted to free enjoyment of light, warmth, and 

 air, which stimulate the development of the adventitious or dor- 

 mant buds along the stem. Decay of the topmost portion of the 

 crown in conifers is invariably quickly followed by the death of 

 the whole stem ; whilst stag-headed, broad-leaved species survive 

 it for many years. The preventive measures mainly consist in 

 the preservation of the layer of dead foliage on the ground, pro- 

 tection of the soil against deterioration by the underplanting of high 

 forests of lightly-foliaged species unable to protect it for them- 

 selves, moderate drainage confined to the removal of surplus 

 moisture only, gradual accustoming of standards to the freer 

 enjoyment of light and air, or avoidance of maintaining individual 

 standards at all. 



Root-rot may also take place in consequence of stagnating 



water and defective circulation of the air in the soil. Under 



normal circumstances, a sufficient degree of aeration takes place 



through the variations of temperature in the upper layers, through 



| the infiltration of moisture charged with oxygen, and through 



I diffusive processes ; but when the exchange or transfusion of 



| gases is hindered, owing to the tenacity of the soil, or to its con- 



| stant wetness, the roots of the plants are apt to be choked, and to 



| rot away, as may be especially noted in regard to many young 



crops of Scots Pine, in which case the rotting of the tap-root is 



I particularly characteristic, whilst the shallower side-roots remain 



1 In some of the public gardens of Munich, endeavours have been made to stop the 

 ; further progress of rot, ensuing after the removal of large branches, by tilling up the 

 j holes with plaster and cement, in order to prevent the lodgment of rainwater and 

 snow, and to cut off the air. Trans. 



