POLYPORUS. 



451 





The mycelium penetrates both bast and rind causing a very 

 acute red-rot in the wood, so that death of the tree attacked 

 rapidly follows. The disease makes its appearance on plants 

 of all ages, and in forests of spruce or pine causes gaps 

 which rapidly extend in a centrifugal direction. The roots 

 and lower parts of the stem are generally the parts first 

 attacked. On the roots, the parasite is easily distinguished, 

 even in the absence of sporophores, 

 by the very delicate white mycelial 

 membranes formed between the 

 bark-scales. Destruction of the 

 wood becomes first evident by the 

 appearance of vertical dark lilac- 

 coloured stripes indicating the stage 

 when the parenchyma cells are 

 killed. At a later stage, the wood 

 becomes, brown, and shows isolated 

 black spots with white margins 

 (Fig. 282). These last consist of 

 coils of dark mycelium surrounded 

 by wood from which the incrusting 

 substance has been dissolved away, 

 leaving only cellulose, readily dis- 

 tinguished by turning blue on 



treatment with chlor-zinc-iodine ; here too, the middle lamellae 

 are ultimately dissolved out, so that the elements become isolated. 

 A colourless mycelium may also be found in the other parts 

 of the wood, both inside the elements, and extending in all 

 directions through the cell-wall, leaving holes where it itself 

 has disappeared. Dissolution of the lignifying substance pro- 

 ceeds from the cell-cavity, the middle lamella remaining 

 intact till the last. The resin of the decayed wood passes over 

 into all healthy parts and flows from the bark of diseased 

 stems as a resin-flux. 



The most effective method for combating the ravages of 

 this parasite is isolation of infected areas. In one case which 

 I investigated in Baden, several spots in the forest formed 

 very evident starting points, and sporophores were everywhere 

 present at the base of stems amongst the moss. Such spots 

 should be enclosed by ditches with vertical sides, and deep 



Fig. 282. — Polyporui annosus. Destruc- 

 tion of Spruce-wood. LoDgitudinal sec- 

 tion showing white (cellulose) spots with 

 black (mycelium) centres, (v. Tubeuf 

 phot.) 



