38 KANSAS UNIVERSITY SCIENCE BULLETIN. 



The endodermis is very conspicuous. (Fig. 36, p.) In 

 cross section the cells are round to oval and from .007 mm. to 

 .045 mm. thick. In longitudinal section they are brick-shaped, 

 on the average .088 mm. in length, and show a distinct nucleus. 

 (Fig. 37, s.) These cells contain protein, and a small amount 

 of starch. Sections stained twenty-four hours in alcannin and 

 in Sudan III and washed with fifty per cent alcohol show all 

 the walls heavily suberized with the exception of from one to 

 three cells bordering the thin-walled parenchyma cells be- 

 tween the bast groups. (Fig. 36.) These cells have com- 

 paratively thin cellulose walls, and they are clearly places of 

 radial conduction. 



The central band of the cortex is composed of collenchyma 

 cells with an average diameter of .022 mm. and an average 

 length of .120 mm. (Figs. 25, q, and 34, ./'.) They have little 

 uniformity in size and shape, with the exception of one layer 

 which lies adjacent to the epidermis and resembles the epider- 

 mis in structure and in cell contents. (Fig. 34.) The cellulose 

 walls contain straight pits. Stomata occur on the stem in con- 

 nection with rather large aerating spaces. Resin ducts occur 

 adjacent to the bast. They are in cross section oval to round 

 in shape, .015 mm. to .045 mm. in diameter, and are sur- 

 rounded by from seven to twelve secreting cells rich in cell 

 contents. 



The epidermis consists of one layer of cells, which have 

 thick cellulose walls. The outer wall is .007 mm. thick and the 

 other walls each .0015 mm. thick. The lumen of the cells is 

 nearly round, and has an average diameter of .011 mm. The 

 epidermal cells contain chloroplasts of the usual type, and 

 granules which show the characteristic stain reaction for pro- 

 tein. There is a very marked cuticle .0045 mm. thick, with 

 deep ridging, which often accompanies great thickness. 

 Stomata the same in structure as the stomata of the leaf are 

 scattered over the surface, on the average nine to the sq. mm. 



The inflorescence is a head surrounded by an involucre of 

 spirally arranged bracts. Before the bud opens a large 

 drop of gum-resin is excreted, which covers the buds 

 with a waxy coating. Small disk flowers occur in the center 

 of the head, surrounded by a circle of golden-yellow ray 

 flowers. A transverse section through the top of one of the 

 involucre bracts is almost round, with a diameter of .52 mm. 



