The BJacl Zones Fanned hy Wood- Destroying Fungi 29 



geivable that siinilai' brown oxidation products may be 

 formed from substances which occur in the free cell sap. In 

 some instances, however, as in cherry wood, the large amount 

 of substance infiltrated in the vessels cannot be attributed to 

 the contents of the parenchyma cells but must come from 

 some other source — i)0=^sibly the cell wall. 



J\Iodern researches have shown that a number of hemi- 

 celluloses occur as carbohydrate reseiwe materials which are 

 deposited in the forui of thickened cell-walls in the endos- 

 perm of seeds and as secondary layers of thickening in the 

 wood parenchyma and wood prosenchyma elements of cer- 

 tain woods. By means of enzymes these reserve materials 

 may be converted into gums and sugars, in which form they 

 may be transported to those parts where growth is taking 

 place. The investigations of Griiss (1896) have shown that 

 a cell-wall which consists of a mixture of two hemicelluloses, 

 is dissolved fractionally by the action of a cytolytic enzyme, 

 that is, one constituent earlier than the other. He found 

 further that the hemicellu loses araban and galactan were 

 transformed respectively into the gums arabin and galactin 

 which conld be transported to tissues even before they were 

 further changed into the sugars, arabinose and galactose. 

 Griiss finds that these gums occur in the dormant reserve ma- 

 terials of the genera Acacia, Astragalus, Prunus, and others, 

 and denotes them as reserve gums. He finds that the result 

 of oxidizing enzymes on the heuiicelluloses is to effect a par- 

 tial digestion of this assimilation product, by which sugar 

 and gum is formed, the amount of gaim varying with the com- 

 pleteness of the digestion. After the resolution of the hemi- 

 celluloses into sugar and gum the sugar is leached out while 

 the gimi is left beliind. Griiss is of the opinion that this 



wood as an oxidation product of their cell contents. He states further 

 that, while possible, it is extremely improbable that substances similar 

 to oxidation products of the cell contents may be excreted by fungi in 

 certain woods. 



