THE INJECTED TRUNKS OF CHESTNUT TREES 487 



Observations. 



The PatJi of tJie Injected Solutions in the Trees. 



As stated before, the path of the sokitions usually was through 

 the vessels of the youngest ring of wood (Figs. 2. 5, 10, and 11). 

 It sometimes happened that the stream was shifted from these 

 vessels. Fig. i shows such a case. This section was cut from a 

 tree which had been injected with methylene blue. The. stain had 

 colored the passages taken by it. The solution of methyene blue 

 was not toxic, but it was stimulating enough to cause the forma- 

 tion of thylloses, which finally plugged the vessels through which 

 the stain passed. The main stream then passed through the vessels 

 of the older year ring. The amount of such shifting appeared to 

 vary with the toxicity of the injected chemical, for killing solutions 

 never changed their paths (Fig. 2). This shifting by removing the 

 source of irritation that is the injected solution from, or bringing it 

 in closer proximity to, the cambium layer had a decided effect on the 

 growth of the cambium and phloem tissues. 



The Wound Tissue Formed. 



The character of the wound tissue depended on the toxicity of 

 the injected solution. Quick killing was not followed by stimulation 

 other than the formation of normal wound tissue (callus) to cover 

 the wound. Fig. 2 shows an instance of this. The section was cut 

 from a branch of a 9-year-old tree, which had been injected in May 

 with meta cresol i-iooo G.M., the branch having been cut in Oc- 

 tober. Callus had formed on both sides of the path of the injected 

 chemical. The photograph shows one side of this path which could 

 be distinguished readily by a stain (s). The callus which had 

 formed is as normal as though the tree had been cut by a knife; 

 the wound cambium or bark cambium (be) surrounds the newly 

 formed tissues; the groups of bast-fiber (bf), the protective cells, 

 have the formation one sees in a one-year-old twig; the phloem (p), 

 cambium layer (c) and xylem (x) are normal. 



There are transitions from such normal wound tissue as that just 

 described, which are caused by the varying toxicity of the injected 



