DISEASES OF TAXODIUM AND LIBOCEDBU8. 



first developed profusely, evidently stops growing. The 

 threads become coated with a brown substance, which also 

 fills many of the cells around the area where active decom- 

 position has taken place, and saturates the cell walls. 

 This humus substance is one of a class known to possess 

 antiseptic properties. These facts suggest that the humus 

 compound described above may in part be the agent which 

 limits the disintegrating effects of the fungus. 



ORIGIN OF THE HUMUS COMPOUND. 



The origin of the humus compounds is still a matter of 

 some uncertainty, owing to the intrinsic difficulties. Friih, 

 who probably has paid more attention to this problem than 

 any other investigator, says that we know as little about the 

 successive stages which a plant member passes through, 

 until peat is formed, as we do of the processes which bring 

 about these changes.* The process is essentially a process 

 of decay. It is at present recognized that decay may be 

 due to chemical processes as such, distinguished from those 

 brought about through the agency of living things. 

 Where decay, or more properly a splitting up of highly 

 complex organic compounds into simpler compounds such 

 as carbon dioxide, ammonia and water, takes place without 

 the aid of bacteria or fungi, it is largely a process of oxida- 

 tion. If access of oxygen is prevented no decay takes 

 place. Hartig,f speaks of the decomposition of plant 

 members following death due to frost, as a process due to 

 the action of oxygen on the dead organic substance ; fungus 

 mycelia get into the tissues after a time and hasten this de- 

 composition. Friih J distinguishes two forms of decomposi- 

 tion not due to chemical changes per se (such as oxidation) ; 

 these he calls " Gahrung " and " Fermententwicklung." 



* Friih, J. J. Uber Torf u. Dopplerit 38. 



t Hartig, R. Zersetzungserscheinungen, etc. 65. 



J Friih, J. J. 1. c. 39. 



37 



