005 



pushed back further from the outer collenchymatous layers. Therefore, 

 cell increase must have taken place in the primary bark. 



The question should now be asked as to whether the tissue, which 

 presses the bast ring away from the wood, is exclusively a product of the 

 secondary bark or whether the wood cylinder itself has contributed to this. 

 We find the answer in the tissue group [hp') which represents the paren- 

 chyma wood. We find such groups of parenchymatous wood within a soft, 

 thin-walled tissue, when bark zvonnds are healed by the formation of new- 

 tissue from the youngest sapwood layers, remaining on the wood body. We 

 learn further, by studying the false annual ring (cf. False Annual Rings) 

 and the healing processes of inner frost tears, to recognize the formation 

 of parenchyma wood from the broken sap wood layer. Also, in the pro- 

 cesses of grafting and especially those of budding and bark grafting we 

 find that cicatrization tissue has been formed from the youngest sap wood, 

 if the actual cambial zone has been injured. If the cambium is retained in 

 an injury but the bark mantle is broken by a tear in the bark, the cambium 

 develops into a tissue, at first parenchymatous, which, at the edge, gradu- 

 ally passes over into a normal wood structure, according to the amount in 

 which the normal bark pressure is restored (cf. Wound Healing). 



The same new growth can also take place on the inner side of the bark 

 if this is raised from the wood c}'linder without an entire interruption of 

 its nutrition. I have carried out the experiment with cherries in sucli a 

 way that the still smooth bark of the young trunks was loosened in strips, 

 connected at their upper ends with the uninjured bark mantel left on the 

 axial cylinder. At the places where the upraised strips passed over into 

 the uninjured bark, I found the same callus formed on the inside which 

 later was differentiated into bark and wood. It has therefore been deter- 

 mined experimentally that exposed -xvood can produce ne-z^' bark and that 

 upraised bark tatters can produce neiv zcood when still attached at their 

 upper end to the wood body. 



In this way. the process in rose canker becomes easily understandable. 

 In the first spring, a tear appears in the bark which extends to the cell rows 

 of the spring wood of the new annual ring already formed and results in 

 the lateral raising of the bark from the cambium as shown in the holes (/). 



At first the constricting influence, wdiich the cork girdle (k) usually 

 exercises on bark and young wood, is wholly overcome because of this cleft, 

 which results in a luxuriant increase of the young wood (on the under side 

 of the figure) where the cambial zone has not been destroyed, and the lux- 

 uriant increase of the j)arenchyma of the inner bark where this had been 

 raised from the young wood (at / on the upper side of the figure). The 

 new structures, whether formed from bark tatters, or }'oung wood, are 

 uniformly callus-like and pass over imperceptibly into one another. It is 

 these new structures which have ruptured the previously continuous bast 

 ring (b, b'), have pressed outward the most strongly injured part (b') and 

 caused its death after splitting it off from the outer bark. 



