834 



wood toward the periphery. The first developmental stages differ according 

 to the life activity of the exposed cells. As a rule, all places on the exposed 

 wood are not covered with sapwood capable of increase. If the tissue of 

 the sapwood does not begin to increase, the cell walls on the edges of the 

 wound swell and turn brown, together with their contents ; they also collapse 

 somewhat and form an irregular thick yellow stripe. The walls in the cell 

 groups, which are adjusting themselves for increase, usually turn brown 

 only slightly and frequently after a short time begin to form wound callus. 

 The thin-walled tissue, gradually growing out in parallel rows (ok), is the 

 wound tissue, the growth conditions of which were described under wounds 

 due to barking. In Fraxinus, for example, this could be observed to be i6 

 cells thick after two days. The arrangement of the callus is comparatively 

 rarely as regular as it is shown in the drawing. Because some parts of the 

 wood do not form wound callus, the adjacent cell rows radiate from one 

 another and cover over the places remaining inactive. This callus forma- 

 tion is so rapid that the covering of the inactive places and the close union 

 of the elements coming from the different sides is a matter of course. 



The bark strips on an average proceed less rapidly to the formation of 

 wound callus. The products of the new formation are also different. To 

 be sure, the peripheral cells, rich in cyptoplasm, project somewhat (k) soon 

 after the operation, but cell increase does not always occur or, in case it 

 does begin, its product is only cork which can protect the wound surface. 

 The formation of new structures is more energetic and increases until an 

 abundant wound callus tissue is formed usually first toward the inner angle, 

 where the bark strip is firmly attached to the wood (ok). 



The rapidly formed wound callus masses of the bark and wood, as well 

 as ultimately those of the scion, unite and in the shortest possible time form 

 a temporary protection for the graft wound. We say "a temporary protec- 

 tion" for, actually, the tissue as yet reproduced is only short-lived. As soon 

 as the the callus tissue has acquired a considerable extent and seems exposed 

 to increasing pressure, a meristem zone is formed in it at a certain distance 

 from the periphery, which at times is strengthened by cork cells. The 

 maturing of this meristem zone depends upon the distance between the stock 

 and scion. At times, at a very short distance, only a few lateral, isolated 

 aggregations may be recognized but when the intermediate space is great 

 and the wound callus formation luxuriant, continuous zones may be discov- 

 ered, which often after having a looped course are connected with the 

 sharply protruding cambial zone of the older overgrowth tissue formed on 

 the bark strips (cCjCc). 



The meristem zone is not drawn in the young wood callus because it 

 does not appear until later. 



In common with the cambial zone of the bark strips (cc), this callus 

 meristem furnishes first of all the actual connecting tissue consisting of 



