dalbey: anatomy of grindelia. 37 



of the xylem have lignified walls. One bundle of average size 

 contained 176 vessels, of an average diameter of .11 mm. The 

 vessels compose 3.74 per cent of the stem. The wood pa- 

 renchyma is scanty in amount. It occurs in radial rows be- 

 tween the vessels and surrounds the inner margin of the 

 bundles. (Fig. 26, y.) These cells contain granules which 

 stain yellow with chlor-zinc-iodide. The wood fibers are of 

 the characteristic type. (Fig. 26, v.) They average .0067 

 mm. in diameter, and are from .045 mm. to .150 mm. long. 

 The walls, on the average .0013 mm. thick, are lignified and 

 distinctly marked by slit-shaped straight pits. 



The line of demarcation between the xylem and the phloem 

 takes a sinuous course, as seen in fig. 25. In the stem near 

 the base of the flower there is an equal amount of xylem and 

 phloem, but in the portion lower down on the stem the ratio 

 of xylem to phloem is 10 to 1. The phloem group is made up 

 of small irregular cells with thin walls (fig. 30), and there 

 is no differentiation into sieve tubes and companion cells. 

 They gradually merge into the cambium layer. (Fig. 22, i.) 

 In irregular masses the stain reaction with aniline sulphate 

 and with safranin is characteristic of lignified walls. A lon- 

 gitudinal section shows lignification, extending in some cases 

 the length of several cells and in other cases only part of the 

 length of a single cell. 



A complete cambium ring is not discernible. 



The medullary rays in stem cross sections are narrow linear 

 zones from two to six cells wide. Their distinguishing fea- 

 ture is a slight radial elongation of the cells. (Fig. 27, b.) 

 The ray cells of the xylem are lignified, and at the sides they 

 are bordered by a mass of xylem parenchyma cells resembling 

 wood fibers in arrangement and in thickness of cell walls. 

 (Fig. 27, c.) In longitudinal section these are brick-shaped, 

 with simply pitted walls, and are usually empty of cell con- 

 tents. 



Within the pericycle exterior to each bundle is a mass of 

 bast tissue. (Figs. 22, n, and 25, s.) Each bast group is 

 radially from five to eight cells in thickness, and its cells are 

 usually pentagonal in cross section. (Fig. 31.) The cell 

 walls, on the average .004 mm. thick, are lignified, and are 

 marked by straight pits. The average length of the bast 

 fibers is about .11 mm., with long, tapering, interlacing ends. 



2 — Univ. Sci. Bull., Vol. IX, No. 3. 



