823 



already formed in the callus, their wood being suggested by strands of short, 

 reticulated vessels (g"). These adjoin the vessels in the wood of the cut- 

 ting, the thin-walled wood cells of which, rich in starch and bounding the 

 pith, have participated in the formation of callus. The old wood of the 

 cutting was torn when cut. The torn place (d) is filled with callus and the 

 cambial zone (c to c) may be traced even into this torn place; it passes 

 through the callus in a connected curve. The normal cambium of the cut- 

 ting lay on the outer side of the wood (h). By cutting off the branch in 

 making the cutting exactly tlie same change has taken place as in the ringed 



caf 



Fig. 198. Rose cutting'. 



branch. At first uniform parenchymatous tissue was formed from the 

 cambium, in which short, reticulated vessels (g) gradually appear. Toward 

 the cut surface these tissue parts have become bounded by a heavy cork 

 layer {k'), but in the outermost bark cells increase has also taken place and 

 in the new tissue a formation of short vascular cells ((/') on the outer side 

 of which is recognizable a meristematic layer (c'). 



In the present example the pith, as well as the cambium, has been the 

 chief centre of callus formation. 



On the other hand, the pith has remained quite inactive in the case of 

 the rose cutting (Fig. 198). 



