BY G. P. DARNELL-SMITH. 879 



consisting of a system of solid or of tubular threads, appears 

 before the spores are formed. The capillitium has l)een described 

 by Harper &, Dodge(9), as originating in vacuolar spaces in the 

 cytoplasm, which elongate and take on the tubular form of young 

 capillitial threads. They find that the capillitium is formed by 

 the deposit of materials in the vacuoles from which the capillitial 

 threads are formed; and that radiating threads run out from 

 the larger granules, which are deposited by the process of intra- 

 protoplasmic secretion. These radiating fibrils suggest, rather 

 strongly, that they are cytoplasmic streams which are bringing 

 materials for the formation of the capillitial wall and its thick- 

 enings, which are laid down as spirals, suggesting that the pro- 

 cess is comparable with the ordinary process of cell-wall forma- 

 tion, but along internal plasma-membranes, rather than external. 



Development of the Spores. 



The stalks bearing the normal spores are unicellular, hyaline, 

 and rich in protoplasmic contents, sometimes excessively so. 



Paraphyses have not been distinguished, though stalks vary 

 much in length; and sometimes old stalks, or stalks upon which 

 the spores have not developed, have the appearance of paraphyses. 

 The spore develops as follows : — 



The stalk elongates, and the spore is abstricted from its end; 

 at this stage, the spore is pear-shaped. 'I'he stalk is slightly cup- 

 shaped at its extremity occasionally, and uni-nucleolate (PL xc, 

 fig.24). The spore increases in size, and becomes binucleolate; 

 at the same time, the stalk shrinks to a mere thread. On their 

 discharge, the spores may show no traces of their point of attach- 

 ment; or each spore may have, still joined to it, a minute thread. 

 The "x" spores develop by abstriction in concatenation from 

 minute hyphaj bordering the loculus of the pycnidium (PL xc, 

 fig.24). 



I am indebted to my assistant, Mr. VV. A. Birmingham, for 

 much careful work during the progress of this investigation. 



Summary. 

 1. " Black Spot" is a serious disease of Citrus fruits in New 

 South Wales, due to the fungus Phoma citricarpa. 



