ZOOLOGY AND BOTANY, MICROSCOPYj ETC. 479 



Growth of Cuttings. — Mr. Francis Darwiu recently read two 

 l^apers at the Linnean Society, on " The Power possessed by Leaves 

 of placing themselves at right angles to Incident Light," and on 

 " The Theory of the Growth of Cuttings, illustrated by observations 

 on the Bramble." Abstracts of the papers have already been pub- 

 lished in the journals to which references are given in the foot- 

 note * 



Function of Chlorophyll, and its relation to Light.t— In pui-- 

 snance of his previous investigations on this subject,^ Professor 

 Pringsheim publishes the results of a new and elaborate series of 

 observations. 



He here adopts a method of separating the colouring matter, 

 together with the fluid or semi-fluid substances which accompany it, 

 from the matrix of the chlorophyll-grain, without the application of 

 any solvent. This is effected by means of a dilute acid,, especially 

 hydrochloric acid, or of the application of a moist heat, as by sub- 

 jecting them to warm water or to the vapour of boiling water. The 

 residue of the chlorophyll-grain then consists of a skeleton of a mode- 

 rately firm substance, the interstices of which had been filled with the 

 fluid or semi-fluid carrier of the colouring matter ; this coloured sub- 

 stance exudes, when heated in the manner described, in the form of 

 green drops. If, however, a dilute acid has been employed, the appear- 

 ance is dilferent from that produced by moist heat, the drops being then 

 of a firmer consistence and of a rusty brown colour. These brown masses 

 gradually assume an angular crystalline appearance, constituting the 

 substance to which Pringsheim has given the name of hypochlorin. 

 The mode in which, it can be obtained shows that hypochlorin is 

 probably decomposed by heat. It evidently exists in the chlorophyll- 

 grains in its natural condition, in addition to the green colouring 

 matter. Were it a product of the action of the acid on the colouring 

 matter, it would make its a2:)pearance equally in all the chlorophyll- 

 grains, which is not the case. 



Professor Pringsheim has paid especial attention to the effects of 

 intense light on the different constituents of the cell. 



The green colour disappears in the course of a few minutes ; but 

 this takes place only when oxygen is present, and not in red light. 

 The resulting substances could not be detected, and are therefore 

 probably gaseous, the products of combustion. The author believes, 

 however, that it is rather a pathological than a normal j^rocess in 

 the cell. Other yellow, blue, and red colouring matters undergo the 

 same changes as that of chlorophyll ; but this is by no means the 

 case with all. 



The colourless matrix of the chlorophyll-grains and the sub- 

 stances enclosed in it are adapted for the double function of the 

 grains, the promotion both of assimilation and of respiration. 

 Among the substances thus enclosed are starch, oil, and especially 



* ' Nature,' xxiii. (1881) pp. 178-81. Pop Sci. Eev., v. (1881) pp. 71-7. In 

 full in Jouin. Linn. Soc. (Bot.), xviii. (1881), pp. 406-19 (2 flgs.). 

 t Jiilirb. wiss. Bot., xii. (1881) pp 288-429 (16 pis). 

 t Bee this Journal, iii. (1880) pp. 117, 480. 



•2 K 2 



