DEFECTS IN THE CHEMICAL PROPERTIES OF WOOD. 155 



not depend on a scarcity of lignin on the cell-walls, but on the 

 presence in their interior of plasma, that has not been con- 

 verted in the cambium and other parenchyma into frost- 

 hardy resting-plasma. The further a plant-part is from the 

 latter condition, the more danger it incurs from autumnal and 

 winter frosts. [The tissues of delicate green-house or hot- 

 house plants, Eucalypti, Pinns palustris, etc., in which growth 

 continues in their native habitat till interrupted by excessive 

 draught, have no resting-plasma ready for the approach of our 

 winters ; they are, therefore, killed by the first moderate frost. 

 Tr.] Hence hardiness against winter-frost, in plants that 

 withstand it normally, depends chiefly on the preceding 

 weather and treatment they have experienced. The prevalent 

 opinion, that after the cells have parted with their contents, 

 and even in dry heartwood, lignification of the cell-wall may 

 still proceed, is in itself highly improbable, owing to the 

 absence of plasma, and has never been proved to be true. 



Abnormal formation of gum, gummosis, occurs in the wood 

 and bark of species of Prunus, as well as in those of certain 

 tropical trees belonging to various natural orders (Acacnt 

 Scm-ifdl said by Gamble to yield true gum-arabic, nankin id 

 rrtnaa, etc.). It is due to metastasis, or chemical transforma- 

 tion into gum of parts of the tissues. 



Resinosis, or conversion of the cell-walls into resin in 

 coniferous wood, has been disproved byMayr* (c./. resin-galls, 

 p. 125). He has also shown that pathological conditions in a 

 tree may cause resin to form. The outflow of resin in logs is 

 not due to metastasis, but is a mechanical process, the resin 

 being pressed out of the resin-ducts by the drying and 

 shrinking wood. In wounded living trees, the flow of resin is 

 a physiological process caused by turgor of the tissues. 



All abnormal tints in wood, whether they result from 

 ferments caused by fungi, or without their action, are due 

 essentially to metastasis, but little is known regarding their 

 origin. 



* H. Mayr, " Das Harz tier Nadelbaiime." 18 ( J4. 



