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XVII. 



WILLOW CANKER : PHYSALOSPOBA {BOTBY08PHMBIA) 

 GBEGARIA, Sacc. 



ByT. JOHNSON, D.Se., F.L.S., Professor of Botany in the Royal 

 College of Science, and Keeper of the Botanical Collections, 

 National Museum, Dublin. 



(Plates XIII.-XV.) 



[Read, December 15 ; Received for Publication, December 18, 1903 ; 

 Published, March 26, 1904.] 



As long ago as the autumn of 1899, I received through the Con- 

 gested Districts Board, from the osier-beds at Letterfrack in 

 Oonnemara, specimens of rods called " black mauls," a commercial 

 variety of Salix triandra, L., which had been rendered useless for 

 basket-making. The rods broke in two owing to the presence, at 

 one or more spots on the rod, of canker* spots. These spots are 

 easily recognisable externally (Plate XIII., fig. 1), and may reach 

 inwards to the pith (Plate XIII., fig. 2). They are weak spots, 

 and cause the rod to snap in two at the least attempt to bend it. 

 The skin of the rod at the spot looks as if it had been scorched ; it 

 is dried up, turns brown, and becomes cracked by the protrusion 

 of very small black specks (Plate XIV., fig. 4) ; later the cracked 

 skin peels off, more or less ; the inner part of the stem becomes 

 exposed, the "cortex" broken up, and the hard bast appears as 

 loose, thread-like strips, sometimes accompanied by a fissure in the 

 disorganised wood reaching to the pith. 



Microscopic examination shows that the canker-spots are the 

 external signs of the permeation, through and through, of the rod 

 by the branching threads of a fungus of which the black specks 

 just mentioned are the fruits. It was not until the autumn of this 

 year that an opportunity was afforded me of seeing to what extent 

 the disease was prevalent in the osier holts, and of obtaining, on 



