298 TAYLOR— ON THE PRODUCTION OF 



Fig. 16. Proliferation in the Phloem-Cambium Region, Polygonum. From Injection 

 No. 6, where Calcium Nitrate in solid form was introduced into the treated 

 intemode. This figure and the next show two phases of the same action. 

 In this one there are two lines of activity, one along "b"-"b," the other 

 more external at "d"-"d." The cells in between were not in an active 

 condition at the time the plant was cut down. At "/" there is a group of 

 wood elements, probably pitted vessels, that have most likely been formed 

 from the iimermost cambial zone. X 55. 



Fig. 17. Xylem Formation from the Pith Cambium. Because of excessively deep 

 staining the details of this preparation were somewhat obscured. At 

 "a" is seen a large pitted vessel. The axis of the vessel is at right angles 

 to the axis of the stem. This is often the case near the wound. The 

 active zone was located at about "b"-'b." The pith cavity is above "d," 

 where the innermost cells are dead and stained dark. The more normal 

 pith is seen to the left. From Injection No. 12, where 1% NH4 OH was 

 used. X 55. 



PLATE LXXVI— THE MAXIMUM DEVELOPMENT OF THE PITH 



CAMBIUM 



Fig. 18. Helianthiis. This specimen was taken from Injection No. 7, treated with 

 1 :1000 G.M. Picric Acid. It shows the point of entrance of the needle. 

 There was no pith cavity formed. There was a considerable reaction here, 

 and the pitted vessels formed from the pith-cambium generally had their 

 axes parallel with that of the stem. The large cell shown at "a" is not a 

 pitted vessel with a horizontal axis, but one of the pith cells that, though it 

 elongated, did not divide. See also Plate LXXVII, Fig. 23. X 11. 



Fig. 19. Ricinus. From Injection No. 1, injected with Picric Acid, 1 :100 G.M. Here, 

 as in Helianthus, the intemode was nearly soHd at the time of the injection, 

 and the little cavity that originally existed was filled by the multipHcation 

 of the pith cells. The xylem shows as a dark band, and is marked "b." 

 The split caused by the needle is marked "(i." X 11. 



PLATE LXXVII— PROLIFERATIONS INTO THE PITH CAVITY AND 

 PHLOEM-CAMBIUM PROLIFERATION 



Fig. 20. Ricinus Pith Proliferations into the Cavity. From Injection No. la, treated 

 with 1:100 G.M. Picric Acid. Note the tuberculate appearance of the 

 proliferated cells. The dark masses ("a") at the bases of some of the 

 enlarged cells are dead cells. X 55. 



Fig. 21. Polygonum Pith Proliferations into the Pith Cavity. From Injection No. 9, 

 treated with 1:50 G.M. Picric Acid. This specimen shows a moderate 

 development of the pith cells. The ends of the cells do not show the 

 tuberculate appearance that was developed in Ricinus. Below the en- 

 larged cellg there may be seen the beginning of a pith cambium. X 55. 



