354 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
spikes of Trifolium repens, Iberis amara, &c. It is due in the first place 
to a more copious nutrition on the side which becomes the most strongly 
developed. 
Unequal Growth in Thickness resulting from position.*— Pursuing 
his researches on epitrophy and hypotrophy. Prof. J. Wiesner arrives at 
the general conclusion that heterotrophy is a compound phenomenon 
resulting from the position of the shoot, not only in reference to the 
horizon, but also in reference to its mother-shoot. With regard to 
whether the heterotrophy is exotrophic or endotrophic, a difference is 
manifested in a general way between Gymnosperms and Angiosperms. 
In most conifers, e. g. the yew, exotrophy is more common ; with most 
Angiosperms, e. g. the lime, endotrophy is the more usual phenomenon. 
Action of the Ultra-violet Rays on the Formation of Flowers ! — 
By observing the action on plants of light which has passed through a 
solution of sulphate of chinine, M. C. de Candolle arrives at the con- 
clusion that, while the ultra-violet rays have the effect of greatly stimu- 
lating the formation of flowers, they are not essential to their develop- 
ment. The experiments were made chiefly on Tropseolum majus ; less 
satisfactory results were obtained with Lobelia Erinus. 
Torsions in the Growth of Leaves and Flowers-! — Herren S. 
Schwendener and G. Krabbe have investigated the causes of the occur- 
rence of these torsions (Orientirungstorsionen), in contrast to hygroscopic 
torsions, in leaves and flowers. They are always the result of external 
forces acting in a specific direction; internal forces can only cause 
curvatures. Those torsions which are caused by gravitation are termed 
by the authors geotortism, to distinguish them from true geotropism ; 
while those caused by the action of light are called heliotortism, as con- 
trasted with true heliotropism. Of the latter we have frequent illustra- 
tions in the stalks of zygomorphic flowers. 
Dr. F. Noll § adduces arguments in opposition to Schwendener and 
Krabbe’s theory of geotortism, and also to Frank’s theory of a polarity 
in cells. He maintains his former contention || that active movements, 
such as those which arise from geotropism, lead to the normal position 
of dorsiventral flowers. As in dorsiventral organs generally, the irrita- 
tion of gravity acts on zygomorphic flowers, so long as they are not in 
their normal position, so as to bring the dorsal side again uppermost. 
The theory of geotortism does not in any way explain this phenomenon. 
Gravity and exotrophy are concurrent factors in the movements under 
consideration. Flowers which have shifted from their normal position 
with respect to the perpendicular by exotrophic movements must be 
restored to it by continuously repeated geotropic movements. 
Secondary Increase in Thickness of Trees.! — Herr L. Jost finds 
that the increase in thickness of the branches of trees is, like their 
* Ber. Deutsch. Bot. Gesell., x. (1892) pp. 605-10 (2 figs.). 
f Arch. Sci. Phys. et Nat., xxviii. (1892) pp. 265-7. 
X Abhandl. Akad. Wise. Berlin, 1892, 165 pp. and 3 pis. See Bot. Centralbl., 
lii. (1892) p. 96. § Flora, lxxvi. (1892), Erganzungsband, pp. 265-89. 
|| Cf. this Journal, 1891, p. 490. 
Ber. Deutsch. Bot. Gesell., x. (1892) pp. 587-605 (1 fig.). Cf. this Journal, 
ante , p. 67. 
