8 REGENERATION 



lasts. This is not strictly correct, since the new shoots formed 

 also contain chlorophyll. But the experiment is terminated 

 before this can cause an appreciable error. It can be shown that 

 the dry weight of shoots or roots regenerated by a leaf or stem is 

 (under equal conditions and in equal time) in direct proportion 

 to the mass of leaves or stems in which regeneration occurs; 

 and this simple relation will be designated briefly as the mass 

 relation. 



The reader will notice that the weight of shoots and roots pro- 

 duced by a leaf or stem is used as a measure of the rate of growth 

 of the shoots and roots. The proportionality between mass of 

 leaves or stems and the mass of shoots and roots produced by 

 them no longer need to hold as soon as the growth of shoots and 

 roots is no longer exclusively or predominantly a function of the 

 assimilating activity of the leaf or stem. 



Whether or not the mass relation is identical with the law of 

 mass action may remain undecided as far as the contents of 

 this book are concerned. The mass relation may certainly be at 

 first the expression of the mass law, since the first anlagen of 

 shoots and roots are equal regardless of the mass of the leaf or 

 stem where the regeneration occurs. The mass of material 

 diffusing into each anlage will increase with the mass of the leaf or 

 stem (provided the light is not excluded), and the concentration 

 of the solutes of the sap in each anlage will as a consequence 

 increase in proportion with the mass of the leaf or stem in which 

 the regeneration occurs. It is quite possible that the growing 

 points of the young shoot will remain small and not vary materi- 

 ally in size during the first growth, and in this case the mass 

 relation will remain identical with the mass law. But if the 

 internodes of the new regenerated shoot grow in thickness the 

 mass of growing cells in a large regenerated shoot will be greater 

 than that in a smaller shoot, and in this case the mass relation 

 may no longer be identical with the mass law. For this reason 

 we shall only speak of the mass relation and not of the mass law. 

 The mass relation, that is, the fact that the mass of shoots and 

 roots regenerated varies in proportion with the mass of the leaf or 

 stem where the regeneration occurs, is suflficiently simple and 

 rationalistic to serve as a guide in the maze of the phenomena of 

 regeneration. 



