ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
229 
lie concludes that the retardation of growth caused by mechanical trac- 
tion on a growing organ is a typical phenomenon of irritation. It is not 
the result of a decrease of hydrostatic pressure in the cells of the organ 
submitted to traction. 
(3) Irritability- 
Movements of Flowers and Leaves.* — Prof. A. Hansgirg adduces 
further illustrations of the following phenomena: — Periodic opening 
and closing of flowers ; ephemeral flowers ; pseudo-cleistogamic flowers ; 
sensitive stamens ; nyctitropic movements and paraheliotropic curvatures 
of leaves ; positively heliotropic curvatures of flower-stalks ; carpotropic 
curvatures belonging to the seven different types ; periodic curvatures 
of flower-stalks ; and nodding of inflorescences. 
Movements of the Flowers of Veronica.f — Herr J. af Klercker has 
observed by means of a camera lucida the movements during flowering 
of those species of Veronica in which the flowers are arranged in spikes 
or racemes. Ho classifies the species examined under four types ; of the 
first V. longifolia may be taken as a good example. 
In this species the axis of the inflorescence and the flower-stalks are 
always brought, before the flowers open, into a definite position with 
respect to the horizon ; and, if disturbed from this position, again return 
to it. This movement ceases after the flowers open. After the opening 
of the flower the style assumes successively three different positions. In 
the first there is a geotropic curvature downwards, the maximum of 
which coincides with the period of maximum growth. In the second 
movement the style again raises itself to a horizontal position ; while in 
the third it again curves downwards, but does not regain this position if 
reversed. This movement is attributed by the author to positive 
geotropism. 
The three other types do not differ essentially from the first, but in 
the fourth, of which V. virginica is an example, the first geotropic 
downward curvature of the style does not take place. 
The author propounds the theory that the power of growth of any 
definite zone of an organ is constant. When, therefore, one side of an 
organ increases in length by geotropism, the other side must subse- 
quently grow more rapidly, and the geotropic curvature must be 
neutralized. 
Movements of the Flower-stalk of Cobaea.J — The late Dr. M. 
Scholtz described the changes in position of the flower-stalk of Gobsea 
scandens before and after flowering. During the development of the bud 
it is negatively geotropic and positively heliotropic. Its end bends in a 
horizontal direction, and the calyx opens. The upper side of the stalk then 
grows more rapidly than the under side, and gives the flower a pendent 
position. The flowers are strongly proterandrous, and the two upper 
stamens, which stand in the front of the flower, open before the others. 
Their filaments then curve inwards, and the other three stamens take 
* Bot. Centralbl., lvi. (1893) pp. 257-62. Cf. this Journal, 1893, p. 69. 
f Bih. K. Svensk. Vet.-Acad.*Handl., xviii. (1893) Afd. 3, 29 pp. and 31 figs. 
(German). 
X Beitr. z. Biol. d. Pflanzen (Cohn), vi. (1893) pp. 305-36 (2 pis. and 10 figs.). 
