849 



unite later. The bark must have been removed by gradual rubbing. If the 

 union of the axes takes place of itself, a connected wood covering is depos- 

 ited each year over the place of union. Often rather larger brown pieces of 

 dead bark are incorporated in the surface of the union. This may be 

 explained by the uneven formation of the two axes which have come in 

 contact. If two trunks, covered with bark scales, touch each other,- the 

 most prominent places are rubbed down first and unite, while more deeply 

 lying hollows do not participate in the union but are enclosed by the new 

 tissue. 



In forests and especially spruce and pine tracts, tzvin trunks are fre- 

 quently met with, which, beginning at the base, had united for different 

 distances. Less frequent are the cases in which the upper parts of the main 

 axes of separate origin have grown together. 



A cross section of the base of a twin trunk often shows three centres. 

 In conifers, the middle, third stem has, as a rule, become very resinous. At 

 any rate, the top of the main axis was broken oi^ when young and two 

 lateral eyes have taken over the growth. Instead of forming horizontal 

 branches, these have developed into two top shoots which, after a consider- 

 able number of years, have suppressed the dying main axis and finally over- 

 grown it. Their overgrowth edges have gradually united so that, finally, 

 one single, united cylinder has come from the three axes. 



According to the experiments mentioned under grafting, it may be 

 assumed as a definite fact that a union can take place between parts of indi- 

 viduals of different kinds. Spruces and firs, apples and pears, with each 

 other and on quinces, or almonds and plums, and the like, may serve as 

 examples well known to all. Nevertheless, a limit in the relationship of the 

 plants certainly exists here, beyond which actual coalescence cannot take 

 place in spite of the closest contact and vigorous rubbing. To be sure, a 

 whole list of reports on the union of very heterogeneous plants may be found 

 in the literature on this subject but a part of these statements is based cer- 

 tainly upon erroneous observations^ in which union was assumed where only 

 overgrowth took place. 



Having so fully described the processes of wound healing, we may here, 

 without being misunderstood, express the opinion that the apparently rigid 

 wood body of a tree may be caused to take on all imaginable forms if the 

 tissue produced from the cambium is confined in some way. It can be said 

 figuratively that the wood trunk flows about any ob j ect standing permanently 

 in the way of its growth in thickness ; it grows over it and can enclose it 

 entirely. Examples of so-called encysted stones, fir cones and even animal 

 mummies have frequently been observed. 



We can here omit the enumeration of special cases, since we now 

 possess a number of most interesting books about remarkable trees and all 



1 Moquin Tandon, Pflanzen-Teratologie, Schauer's translation, 1S42, p. 274. 

 Masters, Vegetable Teratology 1869, p. 55. 



