ZOOLOGY AND BOTANY, MIGEOSCOPY, ETC. 283 



Aerotropism.* — Dr. H. Molisch's researches on tliis subject are 

 now published more at length and in great detail. 



Godlewski's Theory of the Motion of Water in Plants.f— Herr 

 A. Zimmermann claims to show that Godlewski's theory is a physical 

 impossibility. The assumption that when water is driven out of the 

 cells of the medullary rays it passes entirely or chiefly into the upper 

 tracheids, and conversely when it is absorbed by these cells, involves 

 a more rapid increase of the air-pressure in the tracheids downwards 

 than can occur in nature. 



Circumnutation of Etiolated Seedlings.| — By experiments on 

 young plants of Polygonum Fagopyrum, Tropaeolum majus, and Bras- 

 sica Napus growing in a warm chamber lighted only with red light, 

 Herr F. Noll has determined that the circumnutation characteristic 

 of twining stems may be induced also in ordinary shoots made to 

 grow abnormally in vital conditions otherwise favourable. He finds 

 in this an explanation of the occurrence of climbing plants in isolated 

 genera of widely separated natural orders. 



Influence of Gravitation on the Movement of Floral Organs. § — 

 M. J. Dufour finds a remarkable diversity in the way in which the 

 floral organs of plants are affected by gravitation, some appearing to 

 be entirely uninfluenced by it. The cause of this diversity appears 

 to be connected with some unknown factors in the way in which 

 geotropism works. 



Insufficiency of the Imbibition Theory. |1 — Herr M. Scheit ad- 

 duces further arguments against the theory that the motion of the 

 sap in wood is due to currents in the cell-walls themselves. These 

 arguments are derived from the extent to which cell-walls increase 

 in size when permeated by water, from the fact that these membranes 

 are, even in the living plant, in a dead state, and from other con- 

 siderations. 



Mechanism of Twining Plants.lT — Herr J. Wortmann proposes 

 the following as an adequate explanation of the phenomena of 

 twining stems. The movement is brought about by a combination 

 of negative geotropism and circumnutation. In every smallest 

 transverse section of the growing part of a twining stem, these two 

 forces combine in such a way that at the apex of the stem circum- 

 nutation is much stronger than negative geotropism, the latter in- 

 creasing in force towards the base, and therefore in older internodes. 

 The consequence of this is a modification of the ordinary movement 

 of growth, each smallest transverse section of the twining stem having 



* SB. K. Akad. Wiss. Wien, xc. (1884) pp. 110-96 (1 pi.). Cf. this Journal 

 V. (1885) p. 96. 



t Ber. Deutsch. Bot. Gesell., iii. (1885) pp. 290-2. Cf. this Journal, v 

 (1885) p. 490. t Bot. Ztg., xliii. (1885) pp. 664-70. 



§ Arch. Sci. Phys. et Nat., xiv. (1885) pp. 413-24. Cf. this Journal, v. 

 (1885) p. 272. 



II Jenaisch. Zeitschr. f. Naturwiss., xix. (1885) pp. 166-73. Cf. this Journal 

 v. (1885) p. 679. ' 



^ Vcrsamml. Deutsch. Naturf. Strassbufg, 1885. See Bot. Ccntralbl xxiv 

 (1885) p. 252. 



