202 PHYTOHORMONES 



results could be interpreted in terms of a local mobilization 

 effect as described above. 



A conclusion of a similar kind may be drawn from the 

 experiments of Cooper (1936) in which lemon cuttings were 

 treated with auxin at the base. If subsequently the basal 

 10 mm. were cut off and the cuttings again treated with 

 auxin no roots were formed, although controls from which 

 the bases were not cut off rooted vigorously. This indicates 

 that the second factor has already been accumulated at the 

 base and was thus removed with the cut-off portion. 



It will be seen from this discussion that in the complex 

 process of root formation many factors are involved. These 

 include auxin, carbohydrates, a group of other substances 

 such as biotin, and the internal factor discussed above. Much 

 further study will be needed to elucidate their interactions. 



F. Root Formation on Other Organs 



Although we have dealt in this chapter only with root 

 formation on stems and hypocotyls, roots will also be formed 

 on the petioles of isolated leaves which have been treated 

 Hke cuttings (for literature and for a list of leaves tested for 

 root formation see Hagemann, 1932, and Graham, 1934). 

 Since leaves form auxin and food materials in light, this is 

 not surprising; it is also evident that addition of auxin will 

 at best speed up root formation on petioles, but not ma- 

 terially change their rooting response in general. 



Root formation on roots might be considered as a special 

 case, but Bouillenne and Went (1933) concluded that this 

 was governed by the same factors as root formation on 

 stems. They found, in Acalypha, that abundant hormone 

 supply led to the formation either of a large number of 

 sparsely branched roots, or of a few roots with numerous 

 laterals, the controls forming only one or two roots without 

 branches. This would indicate that if the excess hormone 

 in the cutting is not used up in the formation of roots on the 

 stem, it will move into the roots and cause the formation 

 of numerous laterals on them. Zimmerman and Hitchcock 



