276 TAYLOR— ON THE PRODUCTION OF 



but little splitting occurring. When the age of the tree or injuries necessi- 

 tate it, cork-cambia form from the deeper soft-bast cells and cause the 

 shedding of fragments of the bark. 



New Tissue Formation in the Phloem of Castanea "Paragon" 



In all of the specimens examined the special development of lignified 

 tissues in the soft-bast occurred in the neighborhood of rather extensive 

 injuries to the cambium. These injuries of course killed the bark and 

 the cambium over a considerable area, and in addition stopped further 

 growth from the cambium for a short distance above and below this 

 area. This distance was never more than five centimeters, except 

 where an injected chemical, passing up just inside of the cambium, 

 caused a more extensive inhibition of growth. The general result did 

 not seem to vary with the cause of the wound. The simplest conditions 

 were those seen in trunks which were healing around a clean mechanical 

 wound (Plate LXXI, Fig. 3). The condition after an injection was 

 similar. Very weak solutions were ineffective. When the solutions 

 were toxic, however, the cambium and bark adjacent to the path of the 

 flaiid were injured, became in time segregated from the healthy bark by 

 a cork cambium, and finally dried up. Healing progressed as in the 

 first case, the abnormalities appearing above and below the wound as 

 before (Plate LXXI, Fig. 2). A more moderate action killed only the 

 cambium and the innermost part of the soft-bast, in which case the 

 abnormal tissues were formed in the bast external to the dead region. 



In the region of inhibited cambial growth it was seen that the cells 

 between the wood and the inner side of the youngest hard-bast ring 

 eventually became lignified, largely forming wood fibers. Except in 

 the limited regions just described, the cambium continued normal growth. 

 Just outside the area of wound inhibition cell division was unusually 

 active, and there was tendency to form along the border of this area 

 a tissue growth similar to the callus that formed rapidly on the sides 

 of the wound. The effect of this activity would be to force aside the 

 bark over the inhibited area, unless in this area there was some means 

 of compensating for the lack of normal cambial growth. To a great 

 extent this is effected thru the formation of lignified patches in the soft- 

 bast. 



The simplest explanation of the origin of the complicated tissue 

 masses produced can best be afforded thru a separate consideration 

 of the nature of the changes in each of the tissues involved. 



