248 



PHYSIOLOGY OF GROWTH AND CONFIGURATION 



deliciosa are about 30 to 70 mm. in length, while those of Vitis velutina may- 

 exceed 100 mm. The individual parts of the region of elongation in the root 

 show unequal rates of growth. The most rapidly elongating portion lies in the 

 center of the region, while the parts above and below grow more slowly. An 

 experiment in which young roots of Viciafaba seedlings were divided (by India 

 ink lines) into ten zones each a millimeter long, the zones being measured after 

 twenty-four hours, gave the following values for the increments of elongation of 

 the respective zones. The temperature was 2o.5°C. and the zones were num- 

 bered from the tip upward. 



Number of Increment of 



Zone Elongation 



mm. 



X 0.1 



IX 0.2 



VIII 0.3 



VII .• 0.5 



VI 1.3 



V 1.6 



IV 3-5 



III ' S.2 



II 5-8 



1 : 1.5 



Fig. 



-Three stages in the elongation of a root of Vicia faba. 



In Fig. 101 are shown three stages in the elongation of the primary root of 

 a Viciafaba seedling. A shows the root divided into millimeter zones, at the 

 beginning of the experiment, and В and С show the same seedling after six hours 

 and after one day, respectively. 



