Stimulation and Correlation. 



121 



131. Location of the motor zone — Germinate a num- 

 ber of peas or beans until the main roots are about 15 

 mm. long. Mark off into 2 mm. intervals by means of a 

 fine thread held by a bent wire and saturated with india 

 ink. Lay a few of the seedlings which have been treated 

 in this manner in moist sawdust, with the roots extended 

 horizontally. Two 

 days later take up 

 and note the re- 

 gion in which 

 curvature has en- 

 sued. 



132. Diageo- 

 tropism of 

 roots — Grow a 

 number of seed- 

 lings of pea or 

 bean in a box of 

 moist sawdust, 

 one side of which 

 has been replaced with a sheet of glass to permit inspec- 

 tion of the contents. After the roots have attained a 

 length of a few centimeters, and lateral branches have been 

 given off, tilt the box at an angle of 45 degrees, and allow it 

 to remain in this position a day or two. Now examine the 

 positions of the apical portions of the roots. What is the 

 general position of the branches of the main root? What 

 reactions ensue in the main root when it is moved from the 

 vertical position, and in the lateral roots when moved from 

 the horizontal? After the inclined position has been main- 

 tained a proper length of time, the glass may be removed and 

 the sawdust taken from around the roots, with a minimum of 

 disturbance, in such manner that their true positions may be 

 made out. 



Fig. 93, — Showingr successive positions of root seedlings 

 of pea placed horizontally. After Pfeffer. 



