930 MorGan: POLARITY AND REGENERATION IN PLANTS 
In the light of these facts and conclusions certain of the state- 
ments that I made in my book on “‘ Regeneration”’ in regard to 
the cause of the development of the apical buds in a piece of the 
willow must be recast. The development of the apical buds of the 
willow, and of other similar plants, and of the basal buds in the 
burdock appear both to be due, not to a dynamic relation (polarity) 
between the two ends of the piece, but to a static condition already 
existing in the piece before its removal, namely, the relative state 
of develepment of its buds. 
From this point of view Sachs’ theory of formative stuffs plays 
no directive part in the regeneration of pieces of the plants. The 
presence of food stuffs enters into the problem only in so far as 
certain parts are supposed to be able to draw on that which is 
present, while other parts (the less developed buds) are not so able 
to make use of the common supply. The flow of these food stuffs 
through the plant appears from this point of view not to be due to 
the stuffs tending to flow of themselves in certain directions, or as 
the result of the action of some outside agent, as gravity, but their 
flow may be simply a question of diffusion from those places where 
they exist in larger amounts to other places where there is not so 
much of the substance present. If the more vigorous and some- 
what older parts can make use of this material more rapidly than 
can the less well-developed parts, there will be a steady flow of 
soluble food substances towards the growing parts, because in 
these regions the material is being more rapidly used up, and hence 
the region is relatively poorer in these materials. The flow is then 
a purely physical problem. This assumption is, of course, not 
different from that usually employed by botanists to account for the 
flow of soluble substances from one part of a plant to other parts. 
It appears, therefore, that polarity in the plant is not the cause 
of the flow of substances through the plant, as Goebel seems t0 
imply in certain parts of a recent article,* nor does polarity appear 
to regulate the development of certain buds and hold others in 
check.+ Possibly some such factor may determine in the growing 
regions of the plant the relative rate of development of certain buds, 
but even this is not certain and remains to be further examined. 
Bryn MAWR COLLEGE. 
* Goebel. Bull. Torrey es 30: 197-205. 1903. Also Biolog. Centralbl. 22: 
— sit lee 481-505. 
t Morgan. Bull. Torrey wht 30: 206-213. 1903. 
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