NEW CELL FORMATIONS IN PLANTS 277 



The Xylem or Wood was stained by the passage of the injection 

 fluid. If the cells adjoining them are not killed by the fluid, the pitted 

 vessels may be filled with tyloses, due in part at least, to the effect of 

 the injection (3). Some substances caused the wood to disintegrate, 

 killing the cambium and stimulating the formation of abnormal xylem 

 patches external to the dead region. The medullary rays in the wood 

 showed no particular reaction. 



The Bundle-cambium as has already been mentioned, stopped growth 

 and matured into lignified elements, mainly fibers (Plate LXXIV, 

 Fig. 12). 



The Phloem formed the greater width of the bark in trees of the age 

 of those examined, and was the part that showed the most pecuHar 

 developments. 



There resulted an active formation of lignified tissues (a) from the 

 simple lignification of soft bast-cells, and (b) by the development from 

 soft-bast cells of meristematic areas that subsequently formed true xylem. 

 These meristematic areas, from their function may appropriately be 

 termed Xyleni-cambia. Since the formation of areas of simple lignifica- 

 tion frequently takes place subsequent to the formation of the xylem- 

 cambia, and in a definite relation to them, the discussion of the xylem- 

 cambia will be given before that of the simpler case. 



The formation of the xylem-cambia in the soft-bast is a condition 

 of fundamental importance. It is interesting from the contrast it pre- 

 sents with Wistaria and other cases where a bundle-cambium originates 

 from the pericambium, as well as with the discontinuous bundles of some 

 of the Curvembryonae, such as the Chenopodiaceae and the Phytolac- 

 caceae, or Mucuna of the Leguminosae (8). In the present case the xylem- 

 cambium formed is not a bundle cambium, producing both phloem and 

 xylem, but forms xylem only, and eventually is completely matured into 

 xylem. Activity begins with the cells adjacent to the outer face of the 

 hard-bast strands only, and proceeds progressively outward. This 

 active zone is continually renewed on the outside by the activation of 

 more soft-bast cells, while on the inside the cells that have been dividing 

 mature into xylem. There was no evidence that the phloem ring of 

 one year was more sensitive than that of any other, except that the 

 outermost part of the phloem was never affected. This remarkable 

 activity may continue for some time, but finally ceases. There may 

 remain a considerable strip of unmodified soft-bast cells between the 

 newly formed xylem patch and the hard-bast strand next outside, or this 

 strip may become lignified as described below. In no case did the entire 



