839 



In concluding this consideration of the healing processes of wounds, it 

 should be emphasized once more that the decision as to the relative value of 

 the grafting method used refers here only to axes at least one year old and 

 already provided with well developed wood. In grafting the soft wood of 

 woody plants, or herbaceous plants, the choice of method may be governed 

 by purely practical considerations. In the coalescence usually so many 

 elements of the cut surfaces (older bark and wood elements in pith) partici- 

 pate in the formation of wound callus that a close union takes place under 

 all circumstances favorable for the plant body, provided, of course, that a 

 sufficient relationship exists between scion and stock. 



The Longevity of Grafted or Budded Individuals. 



It cannot be denied that, aside from the possible action of different 

 peculiarities of the two grafted parts on one another, grafting influences the 

 development of the individual. As Duhamel has already emphasized, the 

 tissue changes at the place grafted will at any rate cause a change in the 

 conductive capacity. The connecting layer will produce retardation of the 

 water conduction and an easier storing up of the descending, plastic ma- 

 terials in the part which consists of wood parenchyma, rich in starch, as also 

 later when the connecting layer is formed from interwoven prosenchyma 

 elements. The results of these changes have already been discussed. 



The limit, up to which different individuals can be united with one 

 another to form a persistent, normally functioning organism, as yet little 

 understood, may be determined by the fact that, in general, only plants of 

 the same natural families can be grafted (or budded) upon one another with 

 any prospect of success. According to all previous experience, this would, 

 however, represent the extreme limit. A sufficient number of examples are 

 known of cases where members of the same family cannot be united perma- 

 nently. In fact, varieties of the same family can remain united for a few 

 years and then in the end break the union, in which case, as a rule, one part 

 dies. It is probable that, aside from the material relationship, a similar 

 biological development is absolutely necessary in the two individuals which 

 are to unite. I, therefore, believe that the different beginning and end of 

 the vegetative phases (leaf formation, setting of fruit, etc.) and the different 

 amounts of water needed by the individuals is very decisive for the perma- 

 nence of even those unions which were successful in the beginning. Often 

 such cases of grafting remain fresh for many months without any firm 

 union. In herbaceous grafting of heterogeneous varieties, or organs, it is 

 found that the scion often continues growth and develops a sickly inflor- 

 escence but finally dies. So far as I have had insight into this matter, no 

 union had taken place. Both parts may have done their best; all their 

 tissues, capable of developing further, can produce new structures and 

 even, in places, a nominal wound callus but a brown stripe extends 

 between the tissue masses of both parts, which shows at once to which 

 individual the tissue in question belongs. The brown stripe is either formed 



