FOREST PROTECTION 115 



The tales of cruisers to the effect that a tract will "be- 

 come punky in ten to fifteen years" do not seem to deserve 

 any credit. 



An old tree is, ceteris paribus, more readily affected, and 

 more apt to be found affected by disease, than a young one. 



C. Beneficial Fungi. 



The symbiosis of certain fimgi with certain trees (dis- 

 covered by Frank) seems to be beneficial to both; possibly 

 essential to both. 



Many of our trees and shrubs are dependent upon cer- 

 tain fungi, at least for such foods as are derived from humus. 

 These fungi consist of delicate, cobwebby threads such as 

 are seen on mouldy bread. These threads spread through 

 the soil and either enter the outer cells of the root or simply 

 form a mantle (Mycorrhiza) about the root. The fungi live 

 upon decaying animal and plant matter, and transfer a por- 

 tion of this food to the root and doubtless secure in return 

 certain benefits from the root. This mutual helpful relation- 

 ship of two plants is termed commensalism. 



The majority of our heaths, evergreens, poplars, willows, 

 beeches and oaks have become dependent upon these fungi 

 and do not thrive in soils where the fimgi are not found. 



Some herbaceous plants, like the Indian-pipe, have be- 

 come entirely dependent upon these fimgi for food and have, 

 as a consequence, lost all their chlorophyll. 



This field of forest ecological study is practically im- 

 touched, though it will form the basis of future silviculture. 

 Certain fimgi might be used, technologically, for the prepar- 

 ation of pure cellulose. 



D. Signs of disease. 



The signs of disease are visible only on a tree, usually, 

 when it is too late to save the patient. 

 These signs are : — 



A. Hypertrophical swellings, f.i., knots on Spanish oak 



and tumors on yellow pine at Biltmore. 



B. Exudations of rosin in galls or in seams. 



C. Appearance of sporophores, which are rare in some 



species, but are frequently seen on diseased red 

 oak, locust, and ash. When decaying holes ap- 

 pear on a tree, the forester is apt to find the 

 whole tree diseased. Yellow poplar trees are 

 sound within one foot, and white oak logs are 

 sound within two feet from the actual end of " 

 a cavity. 



