2T4 TIMBER AND SOME OF ITS DISEASES [chap. 



the cut suiface is lelieved fiom the compressing 

 influence of the coitex and bark, and owhig to this 

 release of pressure it begins to grow out at the edges 

 into a cushion oi '* callus," as shown in Figs. 29 and 30. 

 A very similar '* callus" is formed in the operation of 



2aGsr-73 



Fro 28 —-The same \\\ longitudinal section P, the pitli of stem and brinch on 

 either sxde of this are the tw elve annual z nes of wo d produced during the years 

 1867-78 as marked 1 he cambm n, C, separates these from the cortc\ B 



multiplying plants by " cuttings," so well known to all 

 the cambium at the cut surface of the "shp" or 

 "cutting" is I'elieved from the pressure of the cortex, 

 and begins to grow out more rapidly in the directions 

 of less pressure, and forms the callus. 



