Ill 



A close inspection shows the presence of white strands oq the 

 affected branches. These are rhizomorphic strands and constitute 

 the vegetative portion of the fungus. On older parts the strands are 

 usually thin {'I cm) and frequently pursue a zig-zag course, being 

 seldom branched. As they pass upwards to the younger branches 

 they frequently become thicker (as much as '2 — '25 cm. in diameter) 

 and are repeatedly branched. Here and there a strand may become 

 frayed out on the surface of a branch and pass into line tibriis, be- 

 coming lost to the naked eye. A branch from a strand passes along 

 to a younger twig and growing along the under side of a petiole of a leaf 

 reaches the- under surface of the lamina; here it branches repeatedly 

 and spreads itself over the surface of the leaf until the whole of the 

 under surface of the leaf is covered with a white mass of fine fibrils. 



Here and there occur structures which are larger than the 

 strands, have an irregular outline and frequently form starting points 

 for the origin of fresh strands. 



When a strand comes into contact with an irregularity or rough- 

 ness on the surface of a branch, or when it reaches a young bud, it 

 produces a dense growth. This also occurs when the mycelium of 

 one leaf comes into contact with another leaf. 



The younger parts of the branches suffer severely from the pre- 

 sence of the fungus. 



So efficient is the means of propagation by the strands that when 

 a branch is infected all of the young parts become affected by the 

 strands. 



The Fungus, 



Each strand consists of a central portion or core which is made 

 up of hyphae running longitudinally. These hyphae are hyaline, 

 measure 4-5 microns in diameter and are septate at long intervals; 

 they are sparingly branched and contain no refractive cell-contents. 

 Branches from the innermost hyphae first arise at right angles to the 

 parent hyphae and then, bending around, pursue a longitudinal course- 

 Branches from the outermost hyphae do not for the most part run 

 longitudinally, but project from the central core and give the strand its 

 soft and shiny appearance. 



The larger structures of irregular outline which occur here and 

 there on a strand are composed of dense masses of hyphae and may 

 be looked upon as undifferentiated sclerotia. 



When an affected leaf is placed in a moist chamber in contact 

 with healthy leaves the white mycelium first accumulates a dense, 

 fluffy growth and then spreads to the unaffected leaves. 



