62 KANSAS UNIVERSITY SCIENCE BULLETIN. 



The wood parenchyma also contains glucosides and calcium 

 oxalate crystals. 



The cambium cells are not always discernible, and do not 

 form a complete ring. 



The phloem is made up of a mass of very irregular thin- 

 walled cells (fig. 34), which are not differentiated into sieve 

 tubes and companion cells. These thin-walled cells vary in 

 diameter from .004 mm. to .020 mm. in X. pennsylvanicum, 

 from .005 mm. to .022 mm. in X. amerieanum, and from .005 

 to .020 mm. in X. globosum. 



The phloem is rich in cell centents, containing glucosides, a 

 rather small, amount of protein, and numerous bodies which 

 give the mucilage stain with methylene blue. 



In each species a starch sheath is discernible (figs. 35, 36, 

 37) , the cells containing very large crystals of calcium oxalate 

 (fig. 35, P) and rather large starch grains (fig. 36, T) , which 

 are more numerous in X. amerieanum than in the other species. 

 In transverse section the cells of the starch sheath have an 

 average diameter of .0357 mm. in X. pennsylvanicum, .0270 

 mm. in X. amerieanum, and .0261 mm. in X. globosum. 



The medullary rays vary in width from 3 to 9 cells in X. 

 pennsylvanicum, from 2 to 6 in X. amerieanum, and from 2 to 5 

 in X. globosum, with an average width in number of cells of 

 4.5 for X. pennsylvanicum, 2.5 for X. amerieanum, and 3.4 for 

 X. globosum. The ray cells of the xylem are lignified and have 

 pitted walls. They have an average radial diameter of .0254 

 mm. in X. pennsylvanicum, of .024 mm. in X. amerieanum, and 

 of .027 mm. in X. globosum. 



There is a striking variation in the size and shape of the 

 different bast groups seen in one cross section of a single 

 species (fig. 26). 



In one cross section the bast masses varied in size from a 

 mass .045 mm. in diameter composed of only six cells, to a 

 mass .570 mm. in diameter made up of many cells. All bast 

 cells are lignified with strongly pitted walls .004 to .005 mm. 

 in thickness. 



The parenchyma of the pericycle is composed of large thin- 

 walled cells and contains numerous air spaces (fig. 49). Here 

 frequent resin ducts occur (fig. 49, T) surrounded by, on the 

 average, six very small secreting cells (fig. 50, X) , which are 

 rich in cell contents. They contain a very small amount of 

 protein, small masses which stain a deep blue in methylene 



