282 KANSAS UNIVERSITY SCIENCE BULLETIN. 



STEM. 



S. X. 



Number of vessels in the octant 66 69 



Average diameter of the larger vessels 35 /' 46 ! J - 



Thickness of walls of vessels 3.2 3.2 



Thickness of walls of fibers 5 5 



Lumen of the fibers 6.4 7 



Number of growth rings 3 2 



Sclerenchyma 100 116 



Collenchyma 56 108 



These tables show that, in comparison with the swamp form, 

 the xerophytic form has thicker leaves, larger and more nu- 

 merous water tubes in the stem, and more strengthening tissue 

 in the bark. 



ANATOMY. 



The Leaf. 



The leaves when young are very densely covered with two 

 kinds of hairs. One sort (fig. 1) has a central axis about .24 

 mm. long, consisting of a straight row of elongated cells. This 

 axis bears branches in whorls of three or four, each branch 

 being composed of one or two cells, the longest of these cells 

 being about .17 mm. in length. The other kind of hairs (fig. 

 2, a) are glandular, and consist of a short stalk of one cell sur- 

 mounted by a globular cell about .026 mm. in diameter. The 

 average length of the glandular hairs is .04 mm. 



The lower epidermis is two-thirds as thick as the upper. The 

 outer part of the wall of the upper epidermis is cutinized, as 

 shown by its red color when stained with Sudan III. The 

 inner part of the wall is cellulose. The entire outer wall of 

 the lower epidermis is cellulose, but is covered by cuticle. The 

 guard cells of the stomata are raised a little above the sur- 

 rounding cells (fig. 5), and each guard cell has beneath it two 

 or three relatively small epidermal cells as shown in cross sec- 

 tion in fig. 5, b, and in surface view in fig. 6, b. These cells 

 differ from the surrounding epidermal cells not only in size 

 but also in cell contents, as will be shown in the chemical sec- 

 tion of this paper. In all the leaves examined no stomata were 

 found on the upper epidermis; but in Solereder (p. 780) the 

 statement is made that stomata have been found upon the 

 upper epidermis of this species. Upon the lower epidermis the 

 stomata average 124 to the square millimeter. The average 

 length of the openings of the stomata is .002089 mm. Using 



