i\] HEALING OF WOUNDS r.Y OCCLUSION 215 



Now this callus (Fig. 29, Cat) is in all cases some- 

 thing niore than mere cambium — or rathei, as the 

 cambium extends by cell-divisions from the cut edge 

 of the wound, its outer parts develop into cortex, and 



Fig 29 —The "ame piece of stem four > ears later The cushion like development, 

 Cal^ resulting from the overgrowth of the cambium and cortical tissues of the cut 

 branch, \ as extended some distance from the edges, and is covering m the exposed 

 wood B IS the dead outer cork> tissue mcapible of growth and partially 

 cracked under the pressures exerted by the thickening of the stem The latter is 

 somewhat swollen transversely , owing to the release of pressure m this region, 

 enabling the cambium to devel p a little more actively here , the quicker growth 

 of the occluding cushion in the horizontal direction is due to the same cause 



its inner parts into wood, as in the normal case The 

 consequence is that we have in the callus, slowly 

 creeping out from the margins of the wo'find, new 



