372. 



THE QUARTERLY REVIEW OF BIOLOGY 



It has already been pointed out that 

 very old root hairs which persist on roots 

 have been found by McDougall (5Z) to 

 have a greater diameter, with brown and 

 thickened walls. Watson (84) has noted 

 that on old roots of the sunflower the root 

 hairs may branch. 



A special type of abnormality of root 



usually followed by the formation of a 

 side branch just behind the cap, which 

 may grow out at right angles, or curve, 

 or later resume a direction parallel to the 

 original hair. Zacharias (89) attributed 

 it to. the plasmolysis of the protoplasm 

 by the changed environment, while Rein- 

 hardt attributed it to cessation of growth, 



Fig. 11. Types of Abnormalities in Root Hairs 



hair growth is the so-called cap formation. 

 It was first observed by Wortmann (88), 

 and was later studied by Zacharias (89), 

 Reinhardt (65), and Stiehr (77). It 

 consists in the formation of a new wall a 

 short distance from the tip, cutting off a 

 short portion. In some cases Reinhardt 

 showed several such partitions. It is 



and resumption in a new direction. He 

 correlated it with peculiar type of growth 

 by Krabbe in bast cells. 



Stiehr (77) found a variety of changes in 

 form upon the change of the concentration 

 or the composition of the medium. The 

 writer has found that these changes occur 

 when the root is transferred from satu- 





