PLATE XXI. 



Fig. 49. Cross section of portion of cortex of X. pennsylvanicum. 

 X 200. Q, epidermis; R, collenchyma; S, parenchyma of pericycle; T, 

 resin duct. 



Fig. 50. Cross section of portion of cortex of X. globosum. X 200. 

 U, epidermis; V, collenchyma; W, parenchyma of pericycle; X, resin duct. 



Fig. 51. Longitudinal section of parenchyma of pericycle of X. glo- 

 bosum. X 193. 



Fig. 52. Cross section of parenchyma of pericycle of X. globosum. 

 X 193. 



Fig. 53. Cross section of parenchyma of pericycle of X. globosum. 

 showing resin duct. X 193. Y, parenchyma ; L, resin duct. 



Fig. 54. Trichome from surface of stem of X. globosum. X 193. A, 

 epidermis; B, trichome. 



Fig. 55. Tangential section of epidermis of stem of X. globosum. 

 X 193. C, epidermal cell; D, glucosides. 



Fig. 56. Tangential section of epidermis of stem of X. americanum. 

 X 193. E, epidermis; F, glucosides. 



Fig. 57. Cross section of epidermis of X. americanum. X 193. 

 Fig. 58. Cross section of epidermis of X. pennsylvanicum. X 193. 

 Fig 59. Longitudinal section of epidermis of stem of X. pennsylvani- 

 cum. X 193. 



