1 66 Regeneration 



and remove all the leaves, new shoots will be formed 

 from the two apical buds of the stem, and roots will 

 arise from the most basal nodes ; provided that the stem 

 is suspended in air saturated with water vapour. The 

 growth in such a stem deprived of all leaves is slow. If 

 we remove all the leaves on such a piece of stem except 

 the two at the apical end, the stem will form only roots, 

 but these will develop much more rapidly than on a 

 stem without leaves. If we remove all the leaves 

 except the two at the basal end, the stem will only 

 form shoots (at the apical end) but these will develop 

 much more rapidly than in a leafless stem. Hence the 

 leaves accelerate the growth of roots towards the basal 

 end and inhibit it towards the apical end; and they 

 favour the growth of shoots towards the apical end and 

 inhibit it in the nodes located nearer the base. 



We thus see that while the stem inhibits the growth 

 of the leaves connected with it, the latter accelerate the 

 growth in the stem. Both facts can probably be 

 explained on the same basis; namely, on the assumption 

 that it is the flow of substances from the leaf to the 

 stem which inhibits the growth of the notches and ac- 

 celerates the growth of the buds in the stem. On this 

 assumption it would also follow that the leaves send 

 root-forming substances towards the basal and shoot - 

 forming substances towards the apex of the stem. It 

 also seems to follow from recent as yet unpubHshed ex- 

 periments by the writer that the root -forming substances 



