DALBEY: SOME SPECIES OF XANTHIUM. 63 



blue, and when sections were treated with Sudan III bodies 

 were found in these cells which seemed to be oil. 



The parenchyma of the pericycle contains glucosides, cal- 

 cium oxalate crystals (fig. 53) , and numerous oval bodies (fig. 

 52) which stain for mucilage with methylene blue, and give 

 the characteristic red color with alcannin and Sudan III. 



The collenchyma, in cross section from 4 to 6 cells deep 

 (figs 49, R; 50, V), is composed of comparatively small thick- 

 walled cells with minute air spaces at the corners, which are 

 rather more numerous in X. pennsylvanicum than in X. ameri- 

 canum or X. globosum. In each species the subepidermal layer 

 (figs. 49 and 50) resembles the epidermis and is richer in cell 

 contents than other cells of the collenchyma. 



In cross section (figs. 57 and 58) the diameter of the epi- 

 dermal cells parallel with the circumference of the stem is on 

 the average .0197 mm. in X. pennsylvanicum, .0140 mm. in 

 X. americanum, and .0190 mm. in X. globosum. In longitudinal 

 section the diameter averages .0428 mm. in X. pennsylvanicum, 

 .0516 mm. in X. americanum, and .0460 mm. in X. globosum. 

 The epidermal cells of each species contain numerous glucoside 

 bodies. In tangential section they appear either in the form 

 of single droplets or masses (figs. 55, D; 56, F) , or in the form 

 of clusters of minute droplets. 



Slight cutinization occurs in the outer walls of the epidermal 

 cells. X. pennsylvanicum and X. globosum have a ridged 

 cuticle .0015 mm. in thickness, while the cuticle in X. ameri- 

 canum is of the same thickness but less ridged. 



Two forms of hairs similar to those found on the leaf occur 

 on the stem (fig. 54). In X. pennslyvanicum both forms are 

 very scanty, while in X. americanum there are on the average 

 2.57 large and 4 small linear hairs to the sq. mm., and in X. 

 globosum 1.17 large and 1 small linear hair to the sq. mm. 



ROOT. 



The cross section of the tap root shows a protostele figs. 60, 

 61) with vessels varying in diameter from .025 to .135 mm. in 

 X. pennsylvanicum, from .025 to .150 mm. in X. americanum, 

 and from .015 to .120 in X. globosum. In cross section the ray 

 cells are generally composed of three rows of cells, the central 

 row made up of ray tracheids with bordered pits. All cells of 

 the xylem have lignified walls. 



