8 o 
James Small 
perception have not yet been connected logically as cause and effect; 
they are as yet only frequently concomitant circumstances. The 
presence of “creaming” bodies on the other hand can be connected 
causally with the series of changes which are supposed to result in 
geotropic curvature, and the granular appearance of cytoplasm is 
too well known to require any special demonstration of the presence 
of bodies which may “cream.” Let any reader carefully compare 
the numbers of phenomena which find an explanation under the 
statolith hypothesis with those which find at least a possible and 
reasonable basis in the chemistry and physics of the cell under the 
hydrion differentiation theory, and then say which theory is the 
more scientific. The nature of the geotropic response, if the statolith 
theory be accepted, is one of the most obscure of physiological 
phenomena. 
On the other hand, the hydrion differentiation of the expressed 
sap is an experimentally demonstrated fact in the case of many 
roots and many stem structures 1 . Roots are well known to be 
acidic, beyond a P H 4*5, and the single fact that chlorophyll is 
stable only in a relatively alkaline medium 2 makes the relative 
alkalinity of green stem structures an obvious fact, since there is 
not a more widespread indicator. It may be objected that the 
“reaction” of the cytoplasm has not been investigated, but there 
is no reason for supposing that it is differentiated in the opposite 
sense 3 . 
If the propagation of the gravity stimulus is due to potential 
differences giving an electric current which modifies the permeability 
of the cells 4 , the direction of that current and of subsequent curva¬ 
ture is almost certainly determined by the movement of electrically 
1 See A. R. Haas in Jour. Biol. Chem. 27 , p. 225, 1916; J. Hempel in Compt. 
Rend. d. trav. d. Lab. d. Carlsberg, 13 , Liv. I, 1917; and H. Kappen in Landw. 
Versuchst. 91 , p. 1, 1918 (Abst. in Bot. Abst. II, 4, p. 143. 1918). 
2 Cf. Practical Plant Biochemistry, by M. W. Onslow, pp. 37-38. Cambridge. 
1920. 
3 Cf. A. R. Haas in Bot. Gaz. 63 , p. 232. 1917. 
4 That it is permeability which acts in producing the turgor differences 
seems to be the only alternative left since the viscosity differences recorded 
by Weber ( Oesterr. Bot. Zeitschr. 64 , p. 439. 1914, also Jahrb.f. wiss. Bot. 57 . 
1917) have been shown by Zollikofer (Ber. D. Bot. Gesell. 35 , p. 291. 1917) to 
be founded on faulty experimental methods, while Phillips {Bot. Gaz. 69 , p. 168. 
1920) has shown fairly conclusively that no differences occur in the two sides 
of the stimulated organ, either in water content, or titration acidity, or hydrion 
concentration, or catalase activity, or sugar content, or percentage of nitro¬ 
genous substances. 
