NEW CELL FORMATIONS IN PLANTS 291 



where the injury had been great, there appeared a pecuhar proHferation 

 of the vascular cells. The cells that responded were apparently all 

 from the young, unlignified cells of the phloem, cambium and probably 

 the xylem. In this case there was a partial resumption of the formation 

 of lignified tissue, with the production of a few pitted vessels. Unfor- 

 tunately the specimen was cut too soon for much growth to have oc- 

 curred, and the extent to which the cambium might have regenerated 

 and resumed its normal function was not shown. (Plate LXXV, Fig. 16). 



The Cambium was often retarded in its growth by the injection, 

 this being especially noticeable when the fluid had passed up or down 

 the vascular bundle. Except that they were possibly of a smaller 

 size, the elements produced were not abnormal. See also the condition 

 described under Phloem. 



The Xylem was generally little affected by the injection, this being 

 especially the case if the elements had become the least lignified. If 

 the fluid passed up the protoxylem while the secondary elements were 

 still soft, they took part in the general proliferation around the bundle. 

 The condition is well shown in Plate LXXVIII, Fig. 29. This case 

 was an extreme one. The cambium continued growth, forming a con- 

 siderable amount of secondary wood. If secondary wood had been 

 formed at the time of the injection, there would have been fibers and 

 pitted vessels visible in the mass of dead xylem included in the center 

 of the proHferated area, instead of spiral protoxylem elements only. 

 It is to be noted that the cells which were directly around the vessels 

 were killed by the toxic action of the fluid, and that the cells further 

 back proUferated. This suggests strongly that the effect of the chemical 

 was an indirect one, and that if by some mechanical means a mass of 

 bundle and surrounding pith cells could have been killed the same result 

 would have been produced. 



The Pith was the region of the stem that gave the most interesting 

 results in the way of tissue formation. This was in those specimens 

 that had been injected by the needle method. 



If the fluid was weak, the inner pith cells bordering on the cavity 

 were not killed. If any reaction at all took place as the result of such 

 an injection, it was a simple budding of the cells into the pith cavity. 

 This condition has already been reported, and has been produced by 

 the use of gases (6). The condition of affairs is seen in Plate LXXVII, 

 Fig. 21. 



If, now, the strength of the solution was somewhat greater, there 

 was formed a layer of dead cells Uning the cavity. From behind this, 



