MorcGan: Hyporuesis oF FORMATIVE STUFFS 209 
The buds near the base of the piece may not develop at all. The 
reverse is true in regard to the roots. They appear only at the 
base of the piece. 
On Sachs’ original assumption the development of the leaf- 
buds at the upper end of the piece is due to the accumulation at 
the upper end of some substance that causes them to develop. 
The development of the roots at the lower end is supposed also 
to be due to the presence there of another kind of substance. 
Vochting showed that when the piece is turned upside down prac- 
tically the same result follows; namely, the shoot-buds develop 
at the distal end of the piece, which is now the lower, and roots 
at the proximal end which is now the upper. This and other 
experiments make it highly probable that external factors play a 
very subordinate role in the development. 
Now Goebel, following Sachs, is also at times inclined to 
ascribe the results of this, or of similar experiments, to the flow of 
different substances in the piece in different directions, but the cause 
of the flow is now ascribed to an internal factor, namely, to the 
polarization of the tissues themselves. It is somewhat ludicrous to 
find that while the hypothesis of formative stuffs was first invented 
to explain the polarity of the piece, the polarity is now assumed 
in order to account for the flow of the stuffs. My first question 
then is this: Is there any evidence to show that the polarity of the 
piece determines the direction of the flow of substances in the 
piece? I should also like to ask, is there any evidence to show 
that after the removal of a piece the flow of substances in it con- 
tinues in the same direction as when the piece was a part of the 
plant ? 
In the first place can we account for the regeneration of pieces 
of the stem by means of the presence of formative stuffs, without 
assuming them to flow in definite directions? Let us see where 
such an assumption will lead. We may assume that when the 
piece is cut off certain substances accumulate in it. The excess 
of these substances tends to start the development of the leaf-buds 
and root-buds. Let us further assume that those leaf-buds will 
begin to develop that are the youngest, and these will always be 
those nearer the distal end. As they develop they will, by using 
up the substances present, retard the development of the other 
