ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
G9 
the “ bacteroid-tissue ” gives up its nitrogenous constituents for the 
nourishment of the plant is still obscure. 
(3) Irritability. 
Causes of Sensitive Movements.* * * § — M. L. Claudel regards the 
movements of certain organs in Astericus maritimus, Carlina acanthifolia , 
and Anastatica hierochuntica as hygroscopic. Ceteris paribus , the cells 
or fibres contract under the influence of desiccation in proportion to the 
thickness of their walls ; and the longest fibres are those which contract 
least in their longest dimension. 
Herr W. Pfeifer f considers that the movements of the stamens of 
the Cynareae cannot be explained by imbibition or the elasticity of the 
cell- walls ; they are rather due to the exosmose of soluble substances, or 
to the formation of substances of a smaller osmotic power in the active 
cells. 
Nyctitropic, Gamotropic, and Carpotropic Movements.! — Prof. A. 
Hansgirg gives the results of observations on a very large number of 
species with respect to the various kinds of movement observed in the 
stalks of buds, flowers, and fruits. 
Nyctitropic movements — i. e. daily changes of position of the stalk, 
recurring during the whole period of flowering, which cause the bud or 
flower to bend downwards during the night or in rainy weather, and to 
stand erect, exposed to the sun, and visible to visiting insects during the 
daytime — were observed in many species belonging to many different 
orders. These movements are always most considerable during the 
early period of blossoming. 
Far more common than these are other movements which occur only 
once, before or after the opening of the flower, or during the ripening 
of the fruit : — Gamotropic for the purpose of making the flower visible 
to insects from a distance, and facilitating pollination ; and carpotropic 
for assisting the dissemination of the seeds. The very numerous 
examples of these movements are referred to six distinct types, repre- 
sented by the genera Oxalis , Primula , Veronica, Aloe, Frag aria, and 
Aquilegia. Similar “ hydrocarpic ” movements occur in some aquatic 
plants. The phenomena in question are almost invariably the result of 
a combination of three factors, viz. of geotropic, heliotropic, and spon- 
taneous curvatures, or of only two of these. The heliotropic and 
geotropic curvatures may be either positive or negative, and examples 
are given of all these various combinations. 
In another communication, § Prof. Hansgirg distinguishes seven 
types of carpotropic curvature, viz. those of Oxalis , Primula, Coronilla, 
Veronica, Aloe, Fragaria, and Aquilegia. 
The same author || gives also lists of plants which display the follow- 
ing phenomena : — Periodic curvatures of flower-stalks ; Periodic opening 
* ‘ Observ. s. le mouvement de quelques plantes hygrometriques,’ Marseille, 
10 pp. and 1 pi. See Bonnier’s Rev. Gen. de Bot., iv. (1892) p. 366. 
f Abhandl. K. Sachs. Gesell. Wiss., xvi. (1891) pp. 325-37. 
j Biol. Centralbl., xi. (1892) pp. 449-64. Cf. this Journal, 1891, p. 372. 
§ Ber. Deutsch. Bot. Gesell., x. (1892) pp. 485-94. 
|j Bot. Centralbl., lii. (1892) pp. 385-93. 
