118 SUMMARY OF CURRENT RESEARCHES RELATING TO 



from this maximum towards both ends of the visible spectrum. When the 

 light was sufficiently strong, heliotropic curvatures took place even in the 

 yellow. 



Assumed Decomposition of Carbonic Acid by Chlorophyll.* — Eeverting 

 to this subject, Dr. N. Pringsheim repeats his previous arguments that we 

 have no direct evidence that the colouring matter of chlorophyll is the 

 agent which brings about the decomposition of the carbon dioxide of the 

 atmosphere. So far from the blue and violet rays, which are the most 

 eagerly absorbed by chlorophyll, being the most active in the decomposition 

 of carbon dioxide, they are almost inoperative in diffused daylight. The 

 author also lays stress on the fact that in artificial solutions of chlorophyll 

 obtained from leaves there is no mutual reaction between the colouring 

 matter and the carbon dioxide of the air ; but that, on the contrary, when 

 exposed to light, the chlorophyll loses its colour and gives off carbonic 

 acid ; and experiment proves that the same takes place in every living cell 

 under the influence of light. While pure carbon dioxide produces no 

 effect on the chlorophyll of the living cell, the least trace of oxygen 

 bleaches and destroys it in the course of a few minutes, when exposed to a 

 sufficiently intense illumination. 



Decomposition of Carbonic Acid by Chlorophyll outside the plant.-j- — 

 Dr. N. Pringsheim contests the accuracy of the observations of Eegnard, 

 according to which carbon dioxide was decomposed by a layer of chloro- 

 phyll placed on strips of cellulose. 



He also comments on the statement of Timiriazeff, that a substance 

 can be obtained from chloroi^hyll by reduction by means of hydrogen in a 

 nascent condition, which has the same property of decomposing carbon 

 dioxide ; and points out that if this observer's last observations are correct 

 they altogether contradict his previous statement X with regard to tho 

 coincidence of the maximum of evolution of oxygen with the absorption- 

 band in the red in the spectrum of chlorophyll, and confirms Pringsheim's 

 own views on this subject. § 



(6) Movement. 



Theory of Twining. — In pursuance of the controversy on this subject, 

 Prof. S. Schwendener || replies to the arguments of Wortmann, ^ insisting on 

 the importance of the clasping movement (Greifbewegung) as an element 

 in the causes of twining, this movement not being by any means confined 

 to tho free apical portion of the stem. His observations were made almost 

 exclusively on Calystegia dahurica. He contends that the phenomena of 

 this and other twining plants cannot be accounted for by the operation of 

 nutation and geotropism alone, the comparative rapidity of the movements 

 and their permanent character being evidence of this. The free movement of 

 the apex due to nutation and geotropism may even be entirely suppressed, 

 without the process of coiling altogether disappearing. 



To this Dr. J. Wortmann ** rej)lies, maintaining that Schwendener's 

 theory apj^lies only to cases of coiling round a firm supj)ort, and is in- 

 adequate to explain circumnutations, free ceilings, and homodromous 

 torsions. 



* SB. K. Preiiss. Akad. Wi.ss., 188G, pp. 6.51-02. Cf. this Journal, 1880, pp. 117, 480 ; 

 1881, p. 479 ; 1882, pp. 220, 818 ; 1886, p. 825. 



t SB. Vcrsamml. Deutsch. Naturf. u. Aerzte, Sent. 20, 1886. See Bot. Centralbl., 

 xxviii. (1886) p. 92. 



t See this Journal, 1885, p. 837 ; 1886, p. 1015. § Ibid., 1880, p. 825. 



II SB. K. Prcuss. Akad. Wiss. Berlin, 1886, i)p. 06:3-72. 

 1 See this Jour/.al, 1886, p. 283. 

 ** Bot. Ztg., xliv. (188(0 Pl>- 001-12, 018-25, 033-42, 049-.'3S, 005-73, 081-90 (3 figs. 



I 



