296 TAYLOR— ON THE PRODUCTION OF 



tween the hard-bast strands. The medullary rays are marked "c," the 

 tannin-containing soft-bast cells "d " Three of the rows that these form 

 are shown, the lowest only being marked. X 50. 



Fig. 6. Injected in 1916 with Sodium Hydroxide, 1:1000 G.M. This shows, in 

 transverse section, phloem in the process of lignification. The growth in 

 this specimen was not sufficiently active to produce pitted vessels. In 

 this figure "j" indicates a medullary ray. A narrow hard-bast strand is 

 marked "j"-"j"; the cells did not stain heavily and therefore do not show 

 clearly. They may be distinguished by the dark central spot caused by 

 the refractivity of the wall. The lignified phloem cells, "/, " may be 

 distinguished by their thick walls, the unmodified cell walls appearing 

 dark, but much thinner. These are shown at "m." Three of the rows 

 of tannin cells may be seen, the uppermost passing thru the uppermost 

 "i." Injection 28. X 180. 



Fig. 7. Lignified Phloem, Longitudinal Section. This is a tangential section, show- 

 ing at "o" a medullary ray in end view. Injection 30. X 130. 



PLATE LXXIII— XYLEM FORMED FROM THE BUNDLE-GAMBIA— 



CASTANEA 



Fig. 8. Longitudinal Section of Xylem from the New or Re-formed Bundle Cambium. 

 The hard-bast strand, outside which the xylem was formed is seen at "h." 

 The wood fibers appear at "d." A medullary ray has been marked "e. " 

 At "/" is shown one of the pitted vessels, the wall of another shows at " g." 

 Injection 20. X 50. 



Fig. 9. The Bordered Pits of the Normal Wood Fibers. Longitudinal Section. 

 The field shown here was an unusually favorable one for the demonstration 

 of these pits. The round area about the pore is shouTi. X 610. 



Fig. 10. The Structure of an Individual Xylem Patch. At "a" is located a hard- 

 bast strand. The direction of the pith is toward the bottom of the sheet. 

 It will be easily seen that the xylem is continuous outward from the hard- 

 bast, and that the pitted vessels are mostly in the earlier formed wood, as 

 in the normal stem. The darker area "b" outside of the .\>'lem patch 

 is the region of lignified phloem cells. The lignification here is com- 

 pleted, no cambial zone remaining between the xylem and the lignified 

 phloem. Injection 28. X 75. 



PLATE LXXIV— XYLEM PRODUCTION ORIGINATING IN PHLOEM 



TISSUE— C^ 5r.l NBA 



Fig. 11. Appearance of the Modified Regions when viewed as Opaque Objects. 

 "WTien dealing with a wood as hard as that of Castanea, it is advantageous 

 to be able to recognize the important features without resorting to the 

 preparation of microtome sections. This photograph shows part of a large 

 area as it would be seen if prepared as described on page 274 and viewed 

 with a high-power hand lens. It is difficult to show the hard-bast strands 



