MECHANISM OF CURVATURE OF ROOTS 



8l 



unstimulated root, which is destroyed during the presentation 

 period (See oxidases). 1 



122. Transmission of Geotropic Impulses. The region in which 

 the curvature of roots ensues lies within 2 mm. of the apex 

 of the root and is but slightly separated from the sensory zone. 

 The nature of geotropic impulses is not understood. The path 

 of conduction probably lies along the inner half of the periblem 

 cylinder, and the fibrillae of Ne- 



mec may serve as organs of con- 

 duction through the cells (14). 



The conclusions of Nemec 

 on this subject have not been 

 tested by additional investiga- 

 tions at this time. It is known 

 however, that transmission in 

 roots is influenced directly by all 

 agents which modify the motility _ 



of protoplasm, such as chloro- i 



form and other anaesthetics, and FlG - 36. Changes in tissues of roots 



. . r , . during curvature. I, sections from curved 



the method of conduction is porti< f n of root of Zea mais (hree hours 



therefore different from that ex- after excitation began. 2, same 20 hours 

 hibited by Mimosa, and much less af ' er excitation began. 3, sections from 



rapid. An impulse set up by a cu , rv ; d port ; n of l f f*<^"^ 



r tyhfera 20 hours after beginning of ex- 



shock in Mimosa travels about cit ation. A, A, A, epidermis of con- 



6OO to I ,OOO times as fast as the cave side. B, B, B, epidermis of con- 



geotropic impulse of a root. vex slde> 



123. Mechanism of Curvature of Roots. Germinate a number 

 of peas, beans, or seeds of corn in damp sawdust. When the 

 radicles have attained a length of 3 or 4 cm. fix them in saw- 

 dust, or place in position in damp chamber with the tips pointing 

 nearly upward. Examine at intervals, and as soon as a root 

 shows a curvature of more than 45, cut away the curved por- 

 tion with a sharp razor and fix in acetic alcohol, or Flemming's 



1 Czapek, F. Ueber ein Befund an geotropisch gereizten Wurzeln. 

 Bot. Ges. 15 : 516. 1898. 



Ber. Deut. 



