DISEASES OF TAXODIUM AND LIBOCEDRUS. 



and believes that it consists of decomposition products of 

 wood exposed to the disintegrating influences of the outer 

 air. These products are dissolved by water and penetrate 

 far into the tree, bringing about the characteristic phe- 

 nomena of wound rot. Frank * claims that Hartig has 

 mistaken the nature of this substance, which he says is not 

 a humus compound but wound gum, which acts as a pre- 

 servative. A comparison of Hartig' s figure and the one 

 on PI. 4, fig. 4, will show that in point of appearance the 

 substance described by Hartig and the one in Taxodium 

 cells are alike. I have also found such substances in 

 wounds, and neither these nor the substance in Taxodium 

 are the wood gum which Frank describes. I believe that 

 Hartig is right when he calls them humus solution, but 

 cannot agree that they are active in promoting decomposi- 

 tion. It might be added that Willkomm f ascribes the 

 brown coloration of diseased pine wood to a humus com- 

 pound which he says is formed from the cell-walls when 

 they begin to decompose. 



No substance corresponding to Frank's wound gum could 

 be obtained from the Taxodium. An aqueous extract of the 

 sound wood is yellowish in color, due to some coloring 

 matter akin to cur cumin. A number of analyses made 

 of diseased wood failed to give any substances which might 

 be regarded as preservative. The sole difference so far found 

 between the normal wood and the diseased wood was the 

 constant presence of the humus compounds described in 

 the diseased wood. 



There are numerous instances which illustrate the preserva- 

 tive and antiseptic properties of humus compounds. The 

 preservative powers of peat deposits are well known. Peat 

 is largely if not entirely composed of humus compounds of 

 one kind or another. Its preservative and antiseptic prop- 



* Frank, B. Krankheiten der Pflanzen 1:32. 1895. 

 t Die mikroscopischen Feinde des Waldes 68. 



35 



