204 DISEASES OF CROP PLANTS 



Jamaica, also similar in character, due to 5. musarum Ashby. 

 The description of the perithecia of the Dominica species as given 

 by South suggests its identity with S. repens. 



Symptoms. 



The effects of the disease are usually visible for a longer 

 time in the foliage of the trees than is the case with Rosellinia 

 attack, so that it has the appearance of being slower in its action. 

 This comes from the fact that the root system is in many cases 

 destroyed gradually without the girdling of the collar wliich in 

 Rosellinia disease very often brings the tree to a sudden end. 

 Sometimes a soft rotted patch is seen extending on the bark of the 

 collar, while much of the root system is still sound, but generally 

 the foliage has become thin and yellow, and the tree is in some 

 cases nearly dead before any damage is visible in that region. 



When the roots of a sickly looking tree are laid bare the 

 disease is seen advancing along them in the form of a soft rot of 

 the bark accompanied by a disagreeable smell. On the last 6 

 inches to a foot of the section adjoining the healthy part of a 

 root the surface of the bark shows a greenish black discoloration, 

 behind which the bark is rotted and easily comes away. Roots 

 that have been attacked for some time are devoid of bark, and 

 the wood is dry and blackened. 



Between the layers of the bark, and on the surface of the wood 

 occur fiat branching rhizomorphic strands, which may be 6-7 mm. 

 broad in their older parts. In well-developed examples they 

 divide several times, the main branches keeping their ribbon-like 

 form and being mostly blunt and rounded at the tips. They 

 may, however, develop a secondary system of finer semi-flattened 

 branchlets along their margin, producing a sort of fishbone 

 pattern. The advancing tips of the strands are whitish and 

 papery ; further back the strands are brownish red and rather 

 fleshy in consistency ; still further back the colour becomes 

 dark brown. When old they lose their consistency and are with 

 difficulty recognisable as blackish streaks on the wood or in the 

 bark. 



A light brown discoloration extending deeply into the wood 

 accompanies the advancing strands, and has been seen beginning 

 just in front of their white tips as they penetrated healthy 

 tissue. South describes the development near the collar of a 

 flat sheet, red on the surface and white within, of similar material 

 to that composing the rhizomorphs, and situated in the cortex 

 or in the place of the cambium layer. 



The Fungus. 



The conidial fructifications of the fungus are of the Stilbella 

 (Stilbum) type, and are produced on the margin of the rhizo- 

 morphs, of the mycehal sheet, or from tufts of white mycelium. 



