STUDIES IN PLANT REGENERATION 227 
ther investigations on account of the impossibility of detecting such 
materials, or explaining their flow. 
The following theory is offered as a suggestion only, and does 
not pretend to account for all the phenomena in the field ; but as 
it is to a certain extent approachable by experiment, it may be 
worth while to present it at this point. Inasmuch as the polar 
tendency in a plant may be regarded as one of its hereditary 
qualities, the power to form roots or shoots at any point might be 
ascribed to the presence at such a place of particular enzymes, 
which are responsible for the formation of the organ in question. 
While the fertilized egg-cell would contain both of these enzymes, 
theoretically restricted to the opposite ends of the cell, this is 
not the case with the majority of cells resulting from its division. 
As growth of the plant continues, the shoot-forming enzyme be- 
comes localized at the nodes where buds are being formed, at the 
growing points of the stem, and (in the case of roots which norm- 
ally produce buds) in the neighborhood of the emerging secondary 
roots. Тһе root-forming enzyme, on the other hand, apparently 
remains a permanent constituent of nearly all cambial cells through- 
out the plant. If we can remove the product of the activity of the 
enzyme but leave it behind, the regeneration of the organ becomes 
possible when food and growing cells are present. This would 
account for the fact that a vegetative point, when split longitudin- 
ally or when cut transversely very near the end, is able to replace 
directly what is lost; but when the cut, extending a little farther 
back, presumably removes the enzyme as well, no restoration takes 
place. Instead a lateral organ produced from some other place 
where a sufficient quantity of the enzyme is still retained assumes 
the role of the axial organ which has been lost; or, in the case 
where shoot-buds are excised from a stem, as practically all 
this sort of enzyme has been removed at the same time, no new 
shoots form. 
The root-forming enzyme which is, according to supposition, 
present in nearly all cambial cells is normally prevented from act- 
ing by the fact that the growth is hindered by the surrounding 
cells and perhaps also by the absence of a static food material 
upon which to act. When a cut is made, however, the stimulus 
of the wound rouses the enzyme into activity, the food aggregating 
