i9 1 7l LOEB—BR YOPH YLL UM 



49 



3. Both phenomena 



formation 

 the stem. 



>phyll 



preserved 



very 



localized 



from 



curvature 



of a U with the concave side above. In such stems an extensive 

 and rapid root formation will take place first in the second and 

 fourth nodes behind the leaf on the lower side and also in the most 

 basal nodes. The second and fourth nodes behind the leaf are 



kinds 



curvature 



of the growth of roots. It should be pointed out also that in 

 Byrophyllum the axes of successive nodes are always at right angles 

 to each other, so that the favored nodes, the second and fourth 

 behind the most apical one, all have the same orientation. It is 



structural 



curvature center around 



behind 



otherwise leafless stem. 



4. If in a horizontally suspended stem only one leaf is left at the 

 base of the stem (and on the lower side) the curvature is usually 

 considerably less than in a stem with a leaf in the apex. The 

 curvature in a stem with a basal leaf is confined to the region behind 

 or around the leaf. It harmonizes with our previous statements 

 that in such stems little or no root formation takes place, and that 

 the root formation which occurs is confined to the node opposite 

 the basal leaf and to the basal cut surface. When the piece of 

 internode left behind the basal leaf is long, a more extensive curva- 

 ture may occur than when the piece of internode left is short. 



5. This difference in the influence of the apical and basal leaf 

 can be made more striking when either the flow of substances in the 

 stem is retarded (for example, by incisions in the stem) or when 

 the resistance to the bending is made greater (by removing the 

 cortex on the upper side of a horizontally placed stem whereby the 





