STUDIES IN PLANT REGENERATION одд 
cludes that it is “іп hohem Grade warscheinlich das jede Polaritat 
umkehrbar ist.” 
Later experiment has not, on the whole, confirmed Klebs’s 
position. McCallum * showed that roots could be produced even 
while the part was slowly drying ; no amount of water could bring 
about the formation of roots on the apical end of the Muhlenbeckia 
internode ; and as a final answer to this contention Vochting + has 
written a recent paper, in which, working with the same plants and 
using similar methodsto those of Klebs, he proved the latter's results 
and conclusion faulty. He found that when the twigs of this willow 
were cut into three pieces, all either erect or inverted, the basal piece 
always produced most roots; that less roots were produced in water 
than in moist sand; and that freeing twigs from cork was 
rather a hindrance than an aid to root-production. As a result һе 
re-emphasizes his old position that in the higher plants, at least, 
polarity is a very stable, probably hereditary characteristic which 
it is a difficult matter to reverse. Just what the conditions were 
which caused the unusual position of the organs in the roots 
referred to above, has not yet been determined. 
Goebel in interpreting this polar tendency at first adopted the 
Duhamel-Sachs “formative stuffs" hypothesis. This theory 
held that there are in the plant definite root-forming and shoot- 
forming substances which usually, owing to the action of gravity, 
flow in different directions. The lighter shoot-forming stuffs flow 
upward and their aggregation at a cut causes the appearance of a 
shoot there ; whereas the heavier root-forming substances flowing 
downward account for the growth of roots on such lower ends. 
However the possibility of a flow of both stuffs in both directions 
independent of the action of gravity was finally admitted by Sachs 
to explain the presence of both kinds of organs in tubers and 
seeds. In Goebel’s § later articles, he no longer insists upon dif- 
ferent formative stuffs, but believes the phenomena capable of 
* McCallum 119. 
T Vóchting, ut ка Боа und Polaritüt bei hohern Pflanzen. Bot, 
Zeit. 64: 101-131. 1906. 
{ Sachs, Stoff uis Form der Pflanzenorgane Gesamelte Abh. über Pflanzen- 
physiologie, 2 : 1159- 
} See Mercato be im  Pllanzenreiche. Biol. Centralbl. s Lis seg. 1905; also 
Weitere Studien über Regeneration. Flora 92 : 132 seg. Јат 
