DECAY 1 79 



above statement that all the fungi found in a particular wood 

 either produce the same or even similar diseases, that they are 

 equally active, or that they operate under all conditions ; and it 

 will suffice in this connection to again direct attention to the 

 results obtained by von Schrenk in the case of the hardy Catalpa, 

 with respect to which he shows that soft rot produced by Poly- 

 porus versicolor (L.), Fr., rapidly destroys the heartwood, while 

 the brown rot induced by Polyporus catalpae, von Schr., operates 

 throughout the trunk near its base ; and yet again, while these 

 two diseases produce specific and distinct effects in the living 

 tree (68), there is as yet no fungus known which will grow in 

 the tissue of the catalpa wood after it has been cut and dried, - 

 a fact which readily explains the remarkable durability of this 

 wood and its adaptation to purposes where freedom from decay 

 is a first consideration. 



2. Conditions under which they flourish. In entering upon a 

 discussion of the conditions under which fungi operate in plant 

 tissues, we must assume, as is in reality true in all cases, that 

 the latter contain an appreciable amount of material which may 

 be utilized by the fungus for the purposes of its own nutrition. 

 Such food material is always presented by the cellulose sub- 

 stance of the cell wall, which is thereby broken down and grad- 

 ually removed, though this does not occur usually until other 

 and more available forms of food material have been exhausted. 

 In the second place, the nutrient material stored by the plant 

 for its own sustenance, such as the starches and sugars, are 

 readily attacked by fungi, and so long as they last the invading 

 organism confines its operations chiefly to those regions and 

 particular cells in which such storage is most marked. Apart 

 from such conditions of food supply, which must be held to be 

 of fundamental importance and to be a constant factor under 

 all circumstances, air, temperature, and moisture must also be 

 regarded as essential though variable factors which operate as 

 the real determinants in the growth of the invading organism. 



The active growth of all plants demands an abundant supply 

 of oxygen. In the vast majority of cases this gas is derived 



