THE INJECTED TRUNKS OF CHESTNUT TREES 489 



ment of a portion of Fig, 4. In the center of the photograph in the 

 region of the cambium layer are cambium cells which have changed 

 into xylem. It shows also that the phloem cells are changed into 

 xylem by division and by thickening of the walls. A group of 

 xylem cells has started growth on the far side of a group of bast- 

 fibers. Fig. 6 shows a section from the same tree, in which this 

 situation, exhibited in Fig. 4, is more pronounced. Fig. 7 shows an 

 enlargement of the cambium region (c). Here it can be seen that 

 the rows of bast-fibers are surrounded by xylem. 



The inhibitory effect on the cambium was transitory. In time 

 a new cambium layer formed, arising from phloem cells. It sepa- 

 rated the irregularly formed xylem from the phloem. It formed a 

 wavy row of cells, but its growth was normal. 



Premature Formation of Cork. 



Correlated with the abnormal growth of xylem in the phloem 

 region was a premature formation of cork. This was formed in so 

 striking a manner that the path of an injected solution could be 

 traced on a tree by the raised lumps of cork extending up and down 

 the tree trunks. This cork formation was not in a continuous ridge 

 of tissue, but appeared in irregularly shaped lumps. So certainly 

 was its formation connected with a disturbance of the cambium and 

 phloem tissues, that one could tell by a cursory glance at a smooth 

 barked tree at what points the above mentioned tissues were de- 

 ranged. In the case of the lithium-injected trees, the spectroscope 

 showed the presence of lithium in the cork, showing a connection 

 between the abnormal tissues and the foreign chemical injected into 

 the tree. Fig. 6 shows that the formation of this cork is due to an 

 unusual development of bark cambium from phloem cells. 



Xylem Developed from Phloem Tissue. 



The xylem which had formed by division of the phloem cells, 

 and often appeared to be a form of wound tissue, has been partially 

 described. Fig. 8 shows the development of such xylem. The 

 group of stone cells partially surrounded by xylem was part of a 

 row of such cells. Rows of stone cells often were found in the 



