11' 



PEOCEEDINGS OF THE ACADEMY OF 



[1899. 



poison vine, Rhus Toxicodendron L. A large stem that had for a 

 quarter of a century been attached to an old cherry tree was cut 

 down. From this were many old branches, which had not attached 

 themselves to anything, and had no rootlets, as those attached to 

 the tree had. In none of these latter cases was the wood eccentric, 

 while even quite young branches, rooting to the bark of the cherry 

 tree, were eccentric. Fig. 3 shows a section of the main stem, 

 cut across two feet from the ground, showing the attachment by 

 its numerous fibrous rootlets to the old bark at the back. Fig. 2 is 

 a section of a seven-year-old branch which has not thrown out 

 rootlets. From an examination of a number of stems with and with- 

 out rootlets, the fact was clear that the rootlets decided the eccen- 

 tricity. They evidently introduced nutritious matter from the old 

 bark to which they clung, and the cells nearest 

 to them derived the chief advantage. The con- 

 centric rings would inevitably Aveaken in propor- 

 tion to the distance from the source of supply. 

 If the woody circles had been all of equal thick - 

 Fig. 2. ness the pith would have been in the centre, 



as we see in Fig. 2. 



In the contribution reported in the Proceedings as above cited, 

 the weakened condition of the wood cells, and their over- 

 growth by stronger ones is 

 given to account for the bark 

 often found inside the trunks 

 of Ba uhhiia, Wistar ia, and 

 other woody plants. We 

 see in Fig. 3 how this can 

 easily be brought about. 

 If some good roots in con- 

 nection with healthy leaves 

 should appear in connec- 

 tion with the lobes repre- 

 sented by the heart-shaped 

 figure so as to reinvigo- 

 rate the depauperate wood 

 ^i^- 3- cells, the bark would soon 



meet, and eventually be wholly enclosed. 



It may be added that the fibrous roots of the Poison Vine are 



