THE USE OF SHOOTS FOE PROPAGATING 



175 



Fig. 27 shows the process of healing in the case of a rose- 

 cutting ; s' is the line along which the shoot was cut ; every- 

 thing below this line is newly-formed tissue, or what is usually 

 called callus. This callus has grown out in the form of a 

 thick ring from the original cambium, and has spread from the 

 margin over the cut end of the shoot. We can distinguish in 

 this figure, which represents a longitudinal section, a ridge of 



Fig. 27.— Formation of Callus in a Rose-Cutting. 

 (For explanation see the letterpress.) 



callus (ca) cut radially, and a transversely cut ridge (ca") which 

 runs towards the front and has already coalesced with the ridge 

 (ca'). In this way the pith, it is true, has become covered in ; 

 but this has taken place without any active co-operation of its 

 tissue, as it has simply been covered in by the fusion of the 

 ring-like growths of callus, which have grown in from the 

 circumference. In other cuttings, as, for instance, in the case 



