F. J. F. SHAW 41 
The Cause of the Disease. 
A microscopic examination of a diseased stem demonstrated the presence of a 
parasitic fungus. The small black spherical bodies visible just below the 
epidermis were the pycnidia of a Diplodia, and the black dust which comes off on 
handling a diseased stem was Diplodia spores. The small white aggregations 
which appear on the surface of a diseased stem are masses of immature hyaline 
Diplodia spores. The spores when mature are dark brown, bicellular bodies 
averaging 24 x 12 withinthe limits 20-294 x 10-15. The pyenidia were rounded 
black structures, about 200-30(p in diameter, with a conspicuous mouth (Pl. H, 
figs. 1, 2) : although numerous and almost touching they do not run together. This 
fungus is evidently identical with that previously described! by Sydow and 
Butler as Diplodia Corchori Syd. and first identified from material collected in 
1910. Earlier than this the fungus had been collected, but not identified 
and named, from a wide area in Bengal including places as far as Kissenganj and 
Mymensingh. It has, however, never before 1917 been observed in such numbers 
as to suggest that it was anything but a stray parasite. 
On splitting open the bark of a diseased stem the surface of the wood is found 
to be coloured a deep brown, and in advanced cases of disease is almost black. 
This discoloration is due to the presence of masses of dark brown hyphe 
of Diplodia running over the surface of the wood. The fibre is similarly 
stained. 
A transverse section of the stem shows that the pycnidia are very 
superficial and occur in the outer layers of the cortex just covered by a few 
layers of cork cells (Pl. LI, fig. 1). The mouths of the pyenidia break through 
this cork covering. The hyphe of the fungus ramify in the cortex and traverse 
the phloem in all directions ; they can frequently be seen following the course 
of a medullary ray as far as the cambium, where hyphe are particularly 
numerous, and in fact this tissue seems to afford a peculiarly favourable medium 
for the growth of the fungus. This accounts for the discoloration of the 
outer surface of the wood in more advanced cases of disease. Hyph also 
penetrate into the wood and are easily visible in section in the cells of the 
xylem. 
From diseased plants the spores of the fungus were obtained and germi- 
nated in pure culture. In culture the fungus forms a copious mycelial growth, 
the mature hyphe being a dirty greyish colour merging into brownish black in the 
old cultures. Up to the present pycnidia have not been formed on artificial 
1 Sydow, H. et P., et Butler, E, J. “ Fungi Indie Orientalis, Pars V.” Annales Uycologici, 
Vol. XIV, 1916, page 196, 3 ‘ 
