14 



"have denied this, and have even said that the place where a graft has 

 healed successfully is the strongest point in the stem. The materials 

 which we have here in hand enable us to put this vexed matter in its 

 proper light. 



It will be noticed that the region about some grafts is more or less 

 swollen by the deposition of an extra amount of wood tissue (due to 

 causes which we need not now discuss), and that the wood in this 

 region is very close grained, as may be seen on careful examination. 

 In some cases when grafts are cut open and dried the tissues crack 

 or check more quickly at other points than at the graft junction, 

 showing that the fibers are stronger in the latter region. It may also 

 be observed when a wind breaks off branches in an old orchard that 

 many, usually a majority, of the fractures occur, not where the grafts 

 have been made, but elsewhere on the same stems, a fact which 

 shows conclusively that the grafts are not points of weakness in those 

 particular cases. 



On the other hand grafts do sometime break, even after they have 

 grown, in apparent health, for a number of years. When a branch 

 breaks at the point of graftage it is prima facia evidence that that was 

 the weakest point in that particular branch. Moreover there are 

 whole classes of facts which the horticulturist has assembled here. 

 Certain kinds of plants are known as a rule to make weak unions, 

 the Clairgeau pear on the quince and the Domestica plum on the 

 peach being examples. A certain nurseryman recently, on my order, 

 sent me ioo " poor unions." These were taken from his nursery 

 rows and were simply sorted out from his stock. In every case the 

 cion. had grown, but the union was bad, /. e., mechanically weak. If 

 the normal union of cion and stock is made by such complete and 

 continuous cylinders of annual growth, how can we account for the 

 unsuccessful unions ? 



The answer is not altogether an easy one. We may approach it 

 by saying that, when the two members are unlike in nature and in 

 some way physiologically incompatible (whatever that may mean), 

 the wound does not heal readily, owing to some sort of irritation 

 which continues to be felt at this point. In nearly all cases this is 

 followed by the deposit of considerable quantities of loose meristem- 

 atic tissue, such as is always produced by the tree for the healing of a 

 wound. These loose and roundish cells fill the space where in a 

 successful graft the long parenchymous cells and ducts interlace. 



