1916] 



ROBERTS— EPIDERMAL CELLS OF ROOTS 



493 



of a cortical cell, and on side / it is exposed directly to the varying 

 external conditions. 



In fig. 2, which is a median section of fig. i, the following factors 

 need to be considered: (i) air medium, (a) the physical character 

 of walls i, 2, 4, 6; (b) the chemical nature of walls i, 2, 4, 6; 

 (c) the osmotic pressure on both 

 sides of walls 2, 4, 6, and inside 

 1; (2) liquid medium, (a) the 

 physical character of walls 1, 

 2, 4, 6; (b) the chemical nature 

 of walls 1, 2, 4, 6; (c) the 

 osmotic pressure on both sides 

 of walls /, 2, 4, 6; (3) length of 

 cells. 



A few measurements were 

 made of the length of walls of 

 cortical cells in comparison with the length of adjoining haired and 

 unhaired epidermal cells. These were taken upon the same corn 



Figs, i, 2. — Fig. 1, form of an epider- 

 mal cell; fig. 2, median section of fig. 1. 



root, the haired epidermal cells being those just above water and 

 the unhaired just below water, with the results shown in table II. 

 These measurements, although few, indicate that there is no 



