374 SCIENCE PROGRESS 



ever, becomes more and more extensively rotted as time goes 

 on, until at length an unusual storm may cause 

 the trunk to snap in two. When a tree infected 

 by Polyporus squamosus has died, the fungus can 

 still continue its annual production of fruit-bodies. 

 It is then a pure saprophyte. With the tree- 

 destroying fungi, which live in the wood, there is 

 usually no hard-and-fast line between parasitism 

 and saprophytism. 



The mycelium of Polyporus squamosus makes 

 its way into the cell-lumina of the infected wood. 

 It does this by boring small holes in the lignified 

 cell-walls. The ends of the hyphae probably ex- 

 crete an enzyme or enzymes capable of rendering 

 soluble the hard membranes. Through holes 

 thus made the fungus hyphae readily pass from 

 cell to cell. In course of time the least lignified 

 cell-walls disappear entirely. The autumn wood, 

 the medullary rays, and the vessels with the 

 sheath of cells around them are the most lignified 

 elements in Sycamore wood, and here they last 

 longest, but become more and more riddled with 

 holes (Fig. 3). At length the wood becomes 

 reduced to a skeleton of its former self. The 

 decay is known as White Rot, because the wood 

 turns much lighter in colour under the action of 

 the fungus. Starch, protoplasm, and cellulose are 

 gradually removed. They are probably rendered 

 soluble by means of appropriate enzymes. This 

 view is supported by an investigation into the 

 enzymes of the fruit-bodies. 1 The following were 



AJ1RB r 1 -i 1 • • 1 



^ found to occur in the expressed juice : laccase, 

 " 3 " „, tyrosinase, amylase, emulsin, protease, lipase, 



Mag. 300. A fibre J j « i n u <.• 



isolated by Schuize's rennetase, and coagulase, whereas negative 

 from^the 1 "rotten results were obtained in the tests for pectase, 

 wood of a Sycamore, maltase, invertase, trehalase, and cytase. How- 

 ceii-waii wenTmade ever, a study of the destruction of wood by the 

 by the mycelium of fungus affords evidence that the mycelium pro- 



Polyporus squamo- . . -iiit a i i 



sus. duces cytase and possibly hadromase. Altogether, 



1 A. H. R. Buller, "The Enzymes of Polyporus squamosus" Ann. of Botany, 

 vol. 20, 1906, pp. 49-59. 



