INFLUENCES AND EFFECTS. 223 



their appearance in species almost innumerable, sending their 

 subtle threads of mycelium deep into the tissues of the woody 

 substance, and the whole mass teems with new life. In this 

 metamorphosis as the fungi flourish so the twigs decay, for the 

 new life is supported at the expense of the old, and together 

 the destroyers and their victims return as useful constituents to 

 the soil from whence they were derived, and form fresh pabulum 

 for a succeeding season of green leaves and sweet flowers. In 

 woods and forests we can even more readily appreciate the good 

 offices of fungi in accelerating the decay of fallen leaves and 

 twigs which surround the base of the parent trees. In such 

 places Nature is left absolutely to her own resources, and what 

 man would accomplish in his carefully attended gardens and 

 shrubberies must here be done without his aid. What we call 

 decay is merely change; change of form, change of relationship, 

 change of composition; and all these changes are effected by 

 various combined agencies water, air, light, heat, these furnish- 

 ing new and suitable conditions for the development of a new 

 race of vegetables. These, by their vigorous growth, continue 

 what water and oxygen, stimulated by light and heat, had 

 begun, and as they flourish for a brief season on the fallen 

 glories of the past summer, make preparation for the coming 

 spring. 



Unfortunately this destructive power of fungi over vegetable 

 tissues is too often exemplified in a manner which man does not 

 approve. The dry rot is a name which has been given to the 

 ravages of more than one species of fungus which flourishes at 

 the expense of the timber it destroys. One of these forms of 

 dry rot fungus is Merulius lacrymans, which is sometimes spoken 

 of as if it were the only one, though perhaps the most destruc- 

 tive in houses. Another is Polyporus hybridus, which attacks 

 oak-built vessels ; * and these are nq$ the only ones which are 

 capable of mischief. It appears that the dry rot fungus acts 

 indirectly on the wood, whose cells are saturated with its juice, 

 and in consequence lose their lignine and cellulose, though their 

 walls suffer no corrosion. The different forms of decay in wood 

 * Sowerby's " Fungi," plates 289 and 287, fig. 6. 



