A. R. Sanderson and H. Sutcliffe 61 



DESCRIPTION OF THE FUNGUS. 



The causative fungus is a species of Sphaeronema which belongs to 

 the group Fungi Imperfecti. 



The mycelium is dark coloured — brownish — the filaments are formed 

 of cells varying much in length compared with the width, much branched, 

 and under suitable conditions as regards moisture, etc. grows rapidly at 

 the expense of the host. Normally the fruiting body, a pycnidium, is 

 produced by the end of the fifth or sixth day after inoculation. These 

 were produced in abundance in cultures in the laboratory in about the 

 same period as on the trees attacked. 



The pycnidium is quite characteristic and should always be looked 

 for in supposed cases of "Mouldy Rot." A pocket lens of powers x 10 

 diameters shows it up quite well. When mature it is a black, flask- 

 shaped body -12 mm. --24 mm. wide at the base and -24 mm.--9 mm. long 

 including the long narrow neck which is -02 mm.--024 mm. wide. The 

 long neck has a distinctly striated appearance due to the presence of 

 thicker portions in the form of strands. At the apex the strands split 

 apart somewhat from the connective tissue (see PI. IV, figs, a and b) 

 facilitating the discharge of masses of pycnidiospores. 



The pycnidia arise directly from masses of the dark coloured my- 

 celium, which with the black pycnidia give the infected surface a black 

 appearance; as the attack progresses this effect is accentuated. Pycnidia 

 are, under favourable conditions produced in immense numbers, many 

 hundreds being crowded together in quite a small area. The pycnidio- 

 spores are produced in the base of the pycnidium, and in a sticky matrix 

 are gradually forced up and out of the neck, adhering when freshly 

 exposed as a white, more or less globular, sticky mass, which rapidly 

 turns brown when dried. 



Eventually the mass is pushed over the side and remains sticking 

 to the outside of the neck, being followed in a very short period — 

 24 hours or more — by a second mass. The masses of pycnidiospores are 

 very quickly affected by desiccation. By the time the mass has turned 

 dark brown, it may be quite a short time after expulsion from the 

 pycnidia, they have lost all power of germination, hence a dry season 

 helps greatly in controlling the disease while a wet one makes it more 

 difficult. This has however proved not always to be the case, as in some 

 cases immense numbers of resting spores are produced when pycnidia 

 are altogether absent during a dry period. The individual pycnidiospores 

 2-5 microns x 4 microns are slightly attenuated and rounded at the ends. 

 When fresh they germinate almost immediately on a suitable medium, 



