178 MANUAL OF THEE DISEASES 



with an undulating, rich brown upper surface bordered at the 

 margin by a narrow white zone (Fig. 27). In wet weather the 

 upper surface becomes mucilaginous. The under surface is 

 more or less fused with the soil. Long white strands of my- 

 celium, arising from the under surface, can be traced to diseased 

 roots. Affected seedlings growing in nursery-beds or in the 

 forest are killed in isolated groups. On pulling the trees, the 

 roots are found to be closely matted with white mycelium. 

 This characteristic, together with the soil being held together 

 by the matted mycelium and the roots being more or less 

 resinous, make this root disease practically indistinguishable 



Fig. 27. — Frmting-bodiea of Rhizinaundidata. 



from the common shoe-string root-rot caused by Armillaria 

 mellea. This latter fungus is common as a root-rotting fungus 

 of both conifers and deciduous trees and sometimes attacks 

 young seedlings (see page 78). Often, however, the fruiting- 

 bodies of the Rhizina occur plentifully around and envelop the 

 stems of affected seedlings. 



Cause. 



The pathogene causing this seedling root-rot is an ascomy- 

 cetous fungus which forms spores in closely packed asci. These 

 stand upright and form the brown upper surface of the fruiting- 

 body. The spores are forcibly shot upward into the air and are 

 blown away. Falling on the ground, they germinate and the 

 abundant white mycelium that is formed penetrates the root- 

 tissues and causes the seedling to die. 



