1288 
the dark and those of the other two groups stimulated again with 
different quantities of light, one group from the same side as before, 
the other from the opposite side. Finally, the curvatures obtained 
were compared. In this way I succeeded in showing that after a 
unilateral illumination sometimes important differences in sensitiveness 
of the posterior and the anterior sides occur. These are greatest in the 
neighbourhood in which the negative curvature begins to arise. 
Further data on this point will be published later. 
We arrive therefore at the conclusion that the curvature away 
from the source of light arises, because the sensitiveness of the 
anterior side diminishes more quickly than that of the posterior and 
consequently the reaction predominates at the back. 
This leads us further to deny the possibility of any direct com- 
parison of this curvature with the negative phototropic reaction of roots 
which is not preceded by a positive one’) and remains on continued 
illumination. We ought therefore henceforth to distinguish the cur- 
vatures of contrary direction which occur in Avena coleoptiles by 
another name. They may be called antiphototropic. 
Is it now possible to explain in the same way the contrary 
curvatures which arise when coleoptiles of Avena are stimulated 
geotropically after preliminary -omnilateral illumination and the negative 
geotropic curvatures which Josr and Miss Srorrper *) were able to 
observe in roots of Lupinus albus which were exposed to high 
centrifugal forces? Evidently not. The difference of pressure must 
always be the same in the cells of the upper and lower side. A 
1) K. Linspaver and V. Vouk. (Zur Kenntnis des Heliotropismus der Wurzeln. 
Vorl. Mitteilung. Ber. d. d. bot. Ges. Bd. 27. 1909) have stated that in roots 
of Sinapis alba and Raphanus sativa small iatensities of light cause positive 
curvatures and greater intensities negative ones. Vouk has described these experi- 
ments somewhat more fully (Zur Kenntnis des Phototropismus der Wurzeln. 
Sitzungsber. d. K. K. Akad. d. Wiss. zu Wien Bd. 121. Abt. J. 1912). It results 
from this that the positive phototropic curvatures which these investigators observed 
in Sinapis alba, arose when there was illumination for 15 hours with an intensity 
of 0.64M.C.; therefore by a quantity of light of 34.560 M.C.S. Vouk on page 503 
gives a table, in which are found different examples of illumination with 128 M.G. 
during 5 minutes, by which means a quantity of light amounting to 38.400 M.G.S. 
was applied. The occurrence of a positive curvature is nowhere mentioned. Moreover 
with illumination lasting 2 minutes no positive curvature arose either. This discre- 
pancy permits us to doubt the phototropie nature of the curvatures found. It is 
moreover quite unintelligible why even in the most favourable case not more than 
119/, of the roots reacted in this manner. 
*) L. Jost und R. Stopper. Studien über Geotropismus Il, Zeitschr. für Bot. Bd, 
IV. 1912. 
