THE USE OF SHOOTS FOR PROPAGATING 185 



their cell-walls, the contents of the outermost layers of cells 

 increasing in amount. 



But it often happens that all the cut surfaces do not take part 

 in the healing processes. If the splint-wood does not show 

 any new cell division, its cell-walls swell up and turn brown ; 

 the outermost cells of the splint-wood then collapse and form a 

 thick irregular brown band. This discolouration is, however, 

 quite slight or does not take place at all if the cells remain, 

 capable of division, and its formative power is so great that 

 already after two days (in the case of the Ash) several layers 

 of callus cells will be formed. 



In the case of the lappets of bark which have been raised 

 from the wood the cells actually forming the cut margins 

 usually die away ; those beneath them may protrude a little, 

 but rarely do more than form protective layers of cork, while 

 the tissues closer to the base of the lappet show active cell 

 division and the formation of healing tissue. But though the 

 exposed layers of cells within the wound only form a moderate 

 amount of new tissue, this is as a rule sufficient to cause a 

 complete temporary closing of the wound. We say a temporary 

 closure, because, as a matter of fact, this first formed tissue only 

 lasts for a short time. For as soon as this healing tissue has 

 attained a certain development and is exposed to a certain 

 pressure, a zone of meristematic tissue arises within it, which 

 unites with the cambium layers which grow out from the angles 

 of the lappets of the bark. This meristem now begins to form 

 the woody parenchyma which covers in the first formed thin- 

 walled closing layers, and which gradually becomes filled with 

 starchy reserve material. 



Finally, the cambium layer of the scion unites with the 

 continuation of the cambium of the stock, and thus a new 

 continuous cambium ring is formed, of which the scion forms 

 an integral part. The transplanted bud has united with the 

 stock and behaves as if it were a bud of the latter (Fig. 28). 



In the adjoining figure, representing a transverse section 

 through a stem of a Rose upon which a bud has been inserted, 

 these conditions are all represented. Wis the wild stock; BL 

 are the lappets of bark, which have been raised by the T-shaped 

 cut ; S is the bud which has been placed within these lappets. 



