60 PROTECTION OF WOODLANDS. 



at any rate partially sound. This phenomenon is more seldom 

 observable in the shallow-rooting Spruce, and hardly ever in the 

 case of any of the broad-leaved species. 



Drainage, removal of layers of moss hindering the penetration 

 of the air, and cultivation of other species less likely to suffer 

 from this special evil, appear to be the best means of obviating 

 danger. 



(3) Diseases in consequence of Atmospheric Influences. 



Frost-shakes and Sun-burn have already been considered (see 

 paras. 8 and 13) as consequences of intense cold and of the 

 action of intense heat on species of trees with smooth bark ; both 

 of these kinds of injuries are usually followed by rot in the 

 vicinity of the damaged places. 



Cankerous diseases are usually caused directly by infection with 

 fungi; but on broad -leaved trees cold can also give rise to the so- 

 called frost-canker, which is characterised by fissuring and scaling 

 of the bark (usually near the ground), and by the formation of 

 excrescences which often also become fissured and scaly. They are 

 especially common on Oaks, but still require more accurate 

 observation and explanation. 



The characteristic leaf-shedding of the Pine should also be con- 

 sidered under this heading, as in the opinion of many investiga- 

 tors it is due to the drying up of the needles, and to the action of 

 frost, although it must also be said that others hold it to be due 

 to a fungus. As this infant ailment or distemper of the Scots 

 Pine, as it has been termed, has increased to an extraordinary 

 extent during the last decades, so as in some localities to assume 

 the proportions of a calamity, and has caused very considerable 

 destruction in nurseries and young crops raised by sowing or 

 planting, its closer consideration may not be out of place here. 



Under leaf-shedding is understood that peculiar disease of the 

 Pine in which the foliage of one to five-year-old plants often in the 

 course of a few days turn brown (unit) and die off, whilst in the 

 case of older plants, only the under branches show signs of IHMH^ 

 affected. The plants attacked, especially the weaker ones, and 

 those growing thickly as in sowings, or one and two-year-old seed- 

 lings in nurseries, often die off to a large extent. Though the sturdier 

 and stronger plants recover to a certain extent, they are unfit for 



