158 



INDIVIDUALITY IN ORGANISMS 



with roots possess, however, not a single root, but a 

 root system which is a composite individual, each root 

 representing a single constituent individual. In such a 

 root system relations of dominance and subordination 

 similar to those in stem systems exist. The formation of 

 each new root represents a reproduction and the estab- 

 lislnnent of a new root individual. In plants possessing 

 a single main root with lateral roots arising from it (Fig. 

 84) this relation appears very clearly. As the main root 

 grows in length directly downward, lateral roots arise 



Figs. 89-91. — Effects of removal or inhibition of main root-tip on 

 direction of growth of lateral roots (from Bruck). 



successively at a certain distance from its growing tip 

 and grow obliquely downward or almost horizontally. 

 Experiments with seedhngs show that if the growing tip 

 of the main root is cut off, new lateral roots arise in 

 larger numbers or nearer the end of the main root, and 

 one or more of these nearest the cut end grows more 

 nearly in the vertical direction downward than when the 

 main growing tip is present (Figs. 89, 90), the behavior 

 differing somewhat according to the level of the cut. 

 Apparently in these seedlings the lateral roots which 



