Diseases of Fruit caused by Fungi 47 



discrimination between primary and secondary causes of disease. In a 

 great many instances the secondary cause of a disease is by far the 

 most obvious, and in many instances in reality is responsible for the injury 

 done; yet but for a primary cause, often of a very trivial nature, the 

 secondary cause could not have come into being. 



The following are illustrations of this condition of things. All the 

 large toadstools and bracket-like fungi so destructive to our orchard and 

 timber trees are known as wound parasites; that is, they can only gain 

 a foothold on the trunk or branch of a tree through a wound. Such 

 wounds may be due to the wind breaking a branch, to a heavy weight 

 of snow, to pruning, &c. In all such cases a wound is produced, and if 

 the scar made by the breaking away of a branch by wind, or by pruning, 

 is left to take care of itself, in all probability some fungus will gain an 

 entrance. On the other hand, if such wounds, as far as practicable, are 

 properly trimmed at once, and thoroughly covered with gas tar, the tree 

 is saved from the attacks of fungi which, if allowed to gain a foothold, 

 speedily work its ruin. 



Hundreds of trees die annually in this country for no obvious reason. 

 From an apparently perfectly healthy condition the leaves commence to 

 wilt and turn yellow early in the season. This condition of things may 

 continue for two or three seasons, gradually becoming worse, until eventu- 

 ally the tree dies. In ninety-nine cases out of a hundred, when a tree 

 shows the symptoms described above, death is due to the presence of a 

 fungus that has entered the tree at the collar. Most of the fungi that 

 cause such diseases are wound parasites, as defined above; but, whether 

 this is the case or not, all fungi are ever ready to take advantage of a 

 wound, rather than have to work their way through an unbroken surface 

 to reach the living portion of the plant, from which they can alone obtain 

 food. The spawn or mycelium of such root- or collar-infesting fungi is 

 present in the soil practically everywhere, and rarely loses an oppor- 

 tunity of entering the tissues of a living plant when conditions are favour- 

 able for so doing. 



The wounds enabling such fungi to gain an entrance into the collar of 

 a tree are due to very varied causes. Over some of these causes we have 

 complete control, if a certain amount of intelligence and care is exercised. 

 In many instances it is certain that hundreds of valuable trees are 

 annually injured, and many eventually killed, by the careless manner in 

 which lawn mowers or grass-cutting machines are handled. A piece of 

 bark from a projecting root, or from the base of the trunk, is torn away. 

 The wound, if noticed at all, is usually covered with soil, so as to hide the 

 scar, and left at that. Fungi present in the soil do the rest. If an accident 

 of this kind does happen, the wound should at once be coated with gas tar. 

 The actual proof that a tree has been, or is being, killed by a fungus in 

 the root or collar is the presence of a white film of spawn or mycelium 

 just under the bark. If a portion of bark is cut away, the white mycelium 

 can be clearly seen. If the disease has not proceeded too far, that is, if it 



