BUNTON: LESQUERELLA SPATHULATA. 197 



section ; figure 38a, a small portion of the epidermis as seen in 

 longitudinal section. 



In the following table is given the average thickness of the 

 cell walls and the average length and width of the epidermal 

 cells : 



Outer tangential wall . 0049 mm. 



Inner tangential wall . 0049 



Radial wall . 003 



Vertical diameter of cavity 0.075 



Radial diameter of cavity 0.026 



Tangential diameter of cavity 0.04 



In the following table is given the average radial breadth of 

 the cork zone, the average thickness of the walls of the cork 

 cells, and the vertical, radial, and tangential dimensions of the 

 cell cavity : 



Average breadth cork zone 15-20 cells. 



Average thickness of wall . 001 mm. 



Vertical diameter of cavity 0.025 



Radial diameter of cavity . 026 



Tangential diameter of cavity 0.036 



Figure 386 represents a few cork cells as seen in cross sec- 

 tion. 



In addition to this large zone of cork there are found in the 

 borke rather large stone cells, which, as shown in figure 39, 

 have relatively thick and pitted walls. 



The tegumentary tissues are remarkably well developed for 

 such a low, herbaceus plant as Lesquerella. When, however, 

 its xerophytic habitat is taken into consideration, the necessity 

 for this provision is readily seen. 



The Strengthening Tissues. — The strengthening tissues in 

 the stem consist of collenchyma, bast fibers, stone cells and 

 wood fibers. 



The radial breadth of the collenchyma zone is 0.093 mm. 

 The average thickness of the walls of the collenchyma cells is 

 0.006 mm. ; the average tangential breadth of the cell cavity is 

 0.036 mm. ; the average radial thickness is 0.01 mm. In figure 

 40 are shown a few collenchyma cells as seen in cross section ; 

 in figure 41 as seen in longitudinal section. 



The sclerenchyma tissue is made up of cells which vary from 

 stone cells to short bast fibers. As shown in figure 42, the stone 

 cells found here are smaller than those found in the borke. 

 Figure 43 represents the stone cells as they appear in longi- 

 tudinal section. 



3-Univ. Sci. Bull.. Vol. V. No. 11. 



