FUNGI 



15 



means neighbouring trees may eventually be destroyed 

 by tlie mycelium spreading originally from a single centre 

 of infection. 



A third mode of attack is practised by certain fungi 

 known as wound-parasites; that is, fungi whose spores 

 are not capable of directly penetrating living tissues, but 

 at first require to live as saprophytes, changing gradually 

 to a parasitic mode of life. This is effected by the spores 

 of such fungi germinating on a wounded surface, as a 

 broken branch, pruned branches, the cut surface of which 

 has not been properly protected, bruises caused by hail- 

 stones, the nibbling of rabbits, mice, etc. The mycelium 

 first produced lives in the decaying tissues of the wound, 

 and gradually attacks the adjoining living tissue. 



Forest and fruit trees are more especially attacked by 

 wound-parasites belonging to the genera Polyporus and 

 allied forms. As a rule, the heart-wood is first attacked, 

 the mycelium gradually extending to the circumference, 

 until finally the trunk becomes quite hollow, owing to the 

 wood being reduced to powder by the corroding action of 

 the mycelium of the parasite. 



Hollow trunks are generally due in the first instance to 

 the attacks of parasitic fungi, and are not, as popularly 

 supposed, the result of old age and what is termed natural 

 decay. 



How THE Spores of Fungi are Dispersed. — Mention 

 has already been made of the dispersal of spores by wind, 

 which must be considered as the most general agent for 

 enabling spores to reach a position suited to their require- 

 ments ; at the same time, experiments indicate that spores 

 are not transported over those immense distances that was 

 at one time considered probable. The influence of wind 



