1916] 



ROBERTS— EPIDERMAL CELLS OF ROOTS 



495 



wall /. Sometimes the branch will be of less diameter than the 

 main hair, as in fig. 8; and again branches will be of equal diameter, 

 as shown in fig. 9. 



The stretched condition of the wall is evidenced by the fact that 

 in some root hairs which are grown 

 in moist air the membranes burst 

 when the hairs are placed in water, 

 or in a solution which has an 

 osmotic pressure lower than that 

 of the root hair cell, as shown in 

 fig. 10; whereas plasmolysis occurs 

 when the root hairs are placed in 

 a solution of higher osmotic strength 

 (fig. n). The root hair remains normal when placed in a solution 

 of an osmotic pressure equal to that of the cell content, as in fig. 12. 



Fig. 7. — Base of the root hair 

 greater in diameter than the rest of 

 the hair. 



Fie. 9 



Figs. 8, 9. — Fig. 8, branch of the root 

 hair of less diameter than the main hair; 

 fig. 9, branches of equal diameter. 



J 



Fig. 



The following forms when grown in 

 moist air and then mounted in distilled 

 water were found to burst immediately: 

 alfalfa, barley, cabbage, mustard, Nas- 

 turtium, radish, Xantkium, and wheat. 

 These when mounted in a solution of 

 sucrose of an osmotic pressure equal to 

 the osmotic pressure of the cell in 



question remain unbroken, whereas plasmolysis occurs if a solution 

 of higher osmotic pressure is used. The cells burst at the tip and 

 a part of the content of the cell is ejected. The nucleus is thrown 



Figs. 10-12. — Fig. 10, root 

 hair grown in moist air and 

 placed in water, membrane 

 burst and content escaped; 

 fig. 11, root hair which has been 

 in a solution of an osmotic 

 pressure higher than that of the 

 root hair; fig. 12, root hair 

 placed in a solution of an 

 osmotic pressure equal to that 

 of the cell content. 



