[ 28l ] 
THE SUPPOSED REVERSAL OF GEOTROPIC 
RESPONSE 
By F. C. NEWCOMBE 
B etween two and three years ago there appeared a series of four 
papers in the New Phytologist by Small (4), Small and Rea (6), 
Small and Lynn (5), and Lynn (3) in which the authors offered experi¬ 
mental evidence for the reversal of geotropic response in the stems 
and roots of seedlings of a number of species of plants. The whole 
work was undertaken for the purpose of securing evidence for Small's 
so-called hydrion differentiation theory of geotropism. With the 
theory itself the present paper has no concern. The hydrion theory 
has been criticised by Blackman (l) and by Snow (7). The experi¬ 
mental data, however, are of such a character as to need consideration 
in themselves. Lack of time prevented the present writer from an 
attempt at verification of the results of Small and his followers till 
a year ago. 
Small, for the support of his hydrion theory, starts with the 
assumption that the protoplasm of stems active in initiating the 
changes in a geotropic response is alkaline in reaction, while the 
corresponding protoplasm of roots is acid. This is a foundation stone 
in the structure of the hydrion theory, and is used to account for the 
difference in behaviour of stem and root to gravitation. 
If now, by any means, the acid and alkaline reaction of the 
protoplasm in root and stem respectively could be reversed, the 
direction of geotropic response should reverse also. So reasons Small. 
To change the reaction of the protoplasm of the root from acid to 
alkaline, Small, after trying other methods, selected the following: 
A piece of flat cork was partially immersed in dilute ammonium 
hydrate for a few days, then allowed to stand for a month under a 
belljar with several changes of air. At the end of this period, the air 
under the belljar would still turn red litmus blue, but was not strong 
enough to kill the seedlings of Vida faba and Zea mais pinned to the 
cork. Many roots turned up; none grew downward. Controls were 
used under other belljars which behaved in the usual way. To 
accompany the text, a plate and several text-figures are shown. 
Passing over the objectionable method of pinning the seedlings 
through the cotyledons or endosperm, it is to be regretted that one 
