60 KANSAS UNIVERSITY SCIENCE BULLETIN. 



two middle cells, and a long, pointed terminal cell (fig. 24), 

 with the outer wall of all the cells sometimes showing distinct 

 papillae. Below the basal cell there are a number of very regular 

 cells (figs. 24, /; 17, Q) , larger than the other cells of the epi- 

 dermis, which in tangential section appear to form a rosette 

 (fig. 17, Q). Both forms of hairs are essentially alike in the 

 three species. The number of the large hairs varies in the 

 three species : in X. pennsylvanicum 22.4 per sq. mm., in 

 X. americanum 53.8, and in X. globosum 46.7. The small linear 

 hairs are numerous over the veins. They are composed of 

 from two to eight cells of about equal size (fig. 22, E) . 



The hairs are distributed in definite relation to the veins, 

 for both large and small hairs always occur in connection with 

 the water-storage tissue above and below the veins (fig. 23, 

 G and H) , those above the intersection of two veins being 

 usually larger (fig 23). The cuticle extends unbroken over all 

 the hairs. 



STEM. 



The young stems are slightly five-angled (figs. 25, 26 and 

 27), a character which seems to be a little more evident in 

 X. pennsylvanicum (fig. 26) than in X. americanum and X. 

 globosum, while older stems are nearly circular in cross sec- 

 tion. At the angles, in the young stems, the parenchyma of 

 the pericycle is not so wide in cross section as elsewhere (figs. 

 25 to 27). At these angles the vascular bundles are larger 

 (figs. 27 and 28) , with xylem in which the rows of vessels show 

 marked radiation (fig. 28). Stems from the three species, of 

 about the same size and age, in cross section show a difference 

 in the comparative amount of each tissue, as indicated in the 

 following tabulation giving radial diameters : 



Collen- Parenchyma 



chyma. of pericycle. Phloem. Xylem. Pith. 



mm. mm. mm. mm. mm. 



X. pennsylvanicum 125 .365 .084 .490 4.531 



X. americanum 125 .318 .131 .693 3.876 



X. globosum 156 .375 .156 1 . 093 3 . 843 



The pith of each species is composed of rather thin-walled, 

 pitted cells (figs. '29, 30 and 31). There is a very slight varia- 

 tion in both longitudinal and transverse diameters of the pith 

 cells of the three species : 



Longitudinal diameter. Transverse diameter. 



X. pennsylvanicum 110 .070 



X. americanum 132 . 071 



X. globosum 118 .076 



