118 MIDDLETOX FUNGI. — GATES. 



a tree where the cambium has been broken, and o^erminate. 

 Wounds of the cambium may be caused by the natural shedding 

 of the lower limbs of a tree, by fires, by windfalls, or in other 

 ways. In all these cases while the wound is being slowly healed 

 over by the growth of the carabial layer it affords an excellent 

 place of entrance for these " wound parasites." When a spore 

 has lodged and germinated, the mycelium at once proceeds to 

 permeate the tissues. It may continue its growth until it has 

 ramified throughout the heart wood, and will then in some 

 species begin its attack upon the sap wood until it has finally 

 permeated the whole tree. 



The mycelium generally grows in three directions along 

 definite lines : — vertically, radially and tangentiall3\ By with- 

 drawino- the moisture content from the wood it causes shrinkage, 

 and thus the wood is broken up into tiny cuboidal blocks. This 

 is the " doty " stage, and the tree may become so weakened as 

 to fall a prey to wind storms which frequently " check " the 

 heart wood. In the radial lines caused by these "checks" the 

 mycelium in some species will grow abundantl}^ forming " punk." 



The tree cannot resist the growth of the m3''celium. Once 

 it has found an entrance it will continue its growth slowly for 

 many years, in some cases for a century. But the tree thus 

 attacked is soon rendered useless for timber, and ultimately 

 must fall. The mycelium generally continues its encroachments 

 upon the cambium, and finally breaks out in fruiting bodies 

 on the surface. These are the shelving hard woody fungi .so 

 frequently seen on the trunks of infected trees. The majority 

 of these wound parasites belong to a family of Hyraenoraycetes 

 known as the Pol3q3oraceffi, characterized, as the name implies, 

 by the presence of numerous poi-es on the under surface of the 

 hymenophore. 



The study of mycology then, has a very important bearing 

 upon the .science of forestry. Canada may well consider this 

 study one of prime importance, as affording a scientific basis for 

 helping to solve the problem of the preservation of our vast forest 

 resources. Surely no more practical subject can engage the 



