490 RUMBOLD— PATHOLOGICAL ANATOMY OF 



phloem region in the injected trees. It can be seen that there is a 

 close relation between the protective cells, i. e., stone cells and bast- 

 fibers, and the xylem which is formed by cell-division of phloem 

 cells. Whether any of these groups of protective cells formed after 

 injection future experiment will show. It seems probable that they 

 did, as according to Moeller (2) such a formation can occur in the 

 normal growth of the chestnut, Castanea vesca. 



An irregular growth of the year ring of wood is shown in Fig. 

 9, which is a section cut from a fourteen-year-old tree injected 

 May, June and July with nitro phenol-para i-iooo G.M. and felled 

 in November. The section shows the year ring of wood only. The 

 formation of xylem on the far side of the bast-fibers is shown in a 

 more pronounced form than in the previously discussed sections. 

 No phloem cells are in this section except bast-fiber and stone cells. 

 The cells on the near side of the bast-fiber groups have been con- 

 verted into xylem by a lignification of their walls. 



Xylem also was formed by the thickening and lignification of 

 phloem cells without cell division. The section shown in Fig. 10 

 was cut from a fourteen-year-old tree, which had been injected in 

 June and July with picric acid i-iooo G.M. and felled in Novem- 

 ber. The cells of the dark-stained groups in the phloem region have 

 lignified cell walls and the shape of phloem cells. This process of 

 lignification is uninfluenced by the proximity of bast-fiber groups. 

 No vessels are formed. It can be seen that the old phloem rings 

 are capable of change, for here the nine-year-old ring shows lignified 

 cells. Fig. II, shows a portion of Fig. 10, enlarged. In Fig. 11, a 

 stone cell has been surrounded by xylem cells of abnormal shapes. 

 The pits in the cell walls can be seen. 



Discussion. 



The investigations of Schilberszky (3) showed that secondary 

 extra-fascicular vascular bundles could be formed on the outer side 

 of the bast-fiber cells in pea and bean seedlings. He found this 

 new tissue developed by the division of the cells of the starch sheath 

 or endodermis. The starch sheath acted as a cambium layer, pro- 

 ducing phloem cells on its outer side and xylem cells on its inner 



