306 



Marine Microbiology 



(2, 25, 30, 32). Cellulohtic activity was proved in other experi- 

 ments by measuring the increase of reducing sugars. 



Attack by fungal hyphae on wood cells can be easily demon- 

 strated by microscopic observation. Considering the type of 

 wood destruction, marine fungi may be called "soft rot fungi" 

 (in the sense of Savory, 51). They decompose mainly the less 

 lignified secondary walls and cause screw-like timnels within 

 the cell walls (2, 60, 30). Because of their dependence on oxygen, 

 the h\'phae mostb^ grow only a few millimeters deep into tlie 

 wood. Onh' in some tropical woods with very large lumina and 

 vessels can fungal hyphae penetrate to the center (6). 



Until now the soft-rot type of deterioration was found only 

 on wood that had been decomposed in the sea, thus, possibly 

 different microorganisms (fungi and bacteria) could be involved 

 in the process of softening. But it was proved by the author tliat 

 pure cultures of marine fungi produce the same screw-like tun- 



20 /u 



:-'<y<y 





'■7 



^^1 



.5* 



\ 



Fig. 2. Balsa wood attacked by a pure culture of Peiitrichospora iniegra 



Linder. In transverse section the tunnels produced by hyphae that are 



growing in the secondary la\'er of the cell wall appear as dark holes. 



