FOREST PROTECTION 93 



canker," Nectria ditissima is by no means confined to that 

 tree, but is the common cause of canker in apple trees, Ash, 

 and many other broad-leaved trees. 



The disease enters by a wound, and the mycelium lives in 

 the rind or cortex, inducing malformation and more or less 

 deep, unsightly, open sores. 



Cankered stems should be removed in the thinnings. 



Protection Against Forest Weeds 



The usual definition of a weed as " a plant out of place " 

 is universally applicable. Under the familiar term are in- 

 cluded all the small growth which causes difficulty in forest 

 cultivation. It thus embraces various grasses, heaths, blae- 

 berry, bramble, raspberry, the coarser ferns, woodbine, etc. 



The damage done by weeds comes under the following 

 heads : 



1. The roots of certain weeds give a matted surface to 

 the soil which may make natural regeneration impossible, and 

 certainly renders cultivation difficult and costly. 



2. Weeds lead to an accumulation of raw humus (i.e. 

 vegetable matter in a dry and unassimilable form), and thus 

 to the diminution of the soil's productive capacity. 



3. Felted fibrous roots hinder the penetration of moisture 

 into the soil, especially when precipitation is in a fine form. 



4. Weeds impede the growth of young forest plants by 

 shading them, causing the air to remain for a long time moist 

 and stagnant about them ; they increase the danger from 

 frost, and frequently overlie and choke young trees. 



5. They harbour injurious animals, particularly mice. 



6. They are the cause of malformations, and those of 

 a twining habit may even strangle young trees. 



The surest means of protection against weeds is by careful 

 management, avoiding sudden heavy thinnings, and long ex- 

 posure of the soil without a wood crop at the time of 

 regeneration, especially on the stronger classes of soil. In 

 afforesting bare land, the work of soil-preparation and plant- 



