470 THE SOOTY MOULD OF CITKUS TREES, 



" Black Blight" among ourselves. It is also often called " Smut " 

 from its appearance, but does not belong to that division of 

 Fungi which includes the true Smuts or UstilayinecK. And the 

 scientific names applied to it have been equally varied, for it 

 assumes a variety of different forms to which different names 

 have been given. In fact this " Sooty Mould " affords a very 

 good illustration of what has been called Polymorphism — the same 

 fungus appearing under different guises at different stages of its 

 development, and it is this feature which will receive special 

 attention here. 



In order to prove the fact of polymorphism it would be necessary 

 to sow pure cultures and watch the development of the different 

 forms under strictly test conditions, for otherwise the forms found 

 together might be really different, and constitute merely a case 

 of association. It is quite conceivable that the exposed surface 

 of an Orange or Lemon leaf might be invaded by a fungus forming 

 a dense felt by the intertwining of its filaments, and this would 

 entangle, like a spider's web, any other spores wafted thither, so 

 that a small community of organisms might be established, not 

 necessarily genetically connected. 



Instead of making artificial cultures, however, I have simply 

 examined a number of specimens under natural conditions from 

 different parts of this colonj^ as well as New South Wales and 

 South Australia, carefully noting the forms found in associa- 

 tion; and when I find a series of forms regularly occurring and 

 constituting this " Sooty Mould," no matter what colony the 

 specimens come from, I am led to the conclusion that they form 

 links in a chain of successive or contemporaneous forms of the 

 same fungus. And I am strengthened in this belief by experi- 

 ments made by Zopf* and others on closely allied species. "Zopf 

 studied his plants chiefly in pure cultures on microscoj^ic slides 

 in nutrient saccharine solutions of various degrees of concentra- 

 tion, and ascertained the agi-eement of the cultivated forms with 

 those which occur in nature." 



N. Act. Leop. xl. 1878. 



