A. SlIARPLES 163 



the stalked form. In the photograph the growing over the stalked form 

 masks the presence of the commoner form. 



CULTURE EXPERIMENTS. 



The Ustulina fructifications found on specimen {B) differed from those 

 previously found in the F. M. S., for a typical conidial layer was formed 

 as in specimens described from other countries. A further difference was 

 observed, for the fungus attacking the w^ood in specimen {A) was isolated 

 and the pure cultures lacked the typical zoning (PI. VI, fig. 17 a) of those 

 obtained by the isolation of the fungus from the rotting tissues at the 

 collar. Again the bored trees showing this fungus were killed very 

 quickly while the collar-rot proceeds very slowly. 



Owing to these differences, critical cultural experiments were under- 

 taken to decide whether there were two distinct species of Ustulina 

 capable of attacking rubber, Ustulina zonafa causing a collar-rot and 

 another species distinct from, but closely related to Ustulina zonata, 

 causing a stem-rot in conjunction with boring beetles. 



TYPICAL CULTURES OBTAINED FROM COLLAR-ROT. 



Pure cultures were first established after numerous failures by taking 

 a small portion of one of the black lines from the collar under sterile 

 conditions and placing it on a block of sterilised Hevea wood in a culture 

 tube. Several days after sowing a greyish mycelium began to grow and 

 spread out slowly over the surface of the block, remaining closely ad- 

 pressed. As the growth continues, the mycelium turns black, forming a 

 thin crust. If the cultures are allowed to develop for several weeks and 

 the blocks taken out and cut open, black lines similar to those formed in 

 the tissues in cases of collar-rot are seen in the middle (PL VIII, fig. 23). 



Small pieces of the black crust from the wood blocks were taken and 

 used to inoculate flask cviltures of potato mush agar. A white flocculent 

 mycelium first develpped; after three or four weeks the surface of the 

 jelly was covered with a black crust similar to that developed over the 

 wood blocks. The crusts in these cultures showed a typical zonation, 

 dark and light zones being formed owing to a thicker aggregation of 

 hyphae at one part than another. 



CULTURES OBTAINED FROM STEM OF SPECIMEN {A). 



A description of symptoms shown by this specimen is given above. 

 The trunk of the tree was sent into the Laboratory and the affected 

 portion cut into sections. The boundary between diseased and healthy 



