y^^S GENERAL CONDITIONS OF PLANT-LIFE, 



From this percentage Gautier deduces the formula Cjg H22 Nj O3 

 relation to that of Bilirubin (Gjg H|g Ng O3). It is of interest to note that iron was not 

 found in either case. The spectrum of Hoppe-Seyler's chlorophyllan is the same as 

 that of chlorophyll.] 



Optical Properties of Chlorophyll. If parts of plants that contain chlorophyll are 

 repeatedly boiled in water and then quickly dried at a temperature not too high and 

 pulverised, a substance is obtained which is easily examined and can be preserved for 

 a long time unchanged. From this powder the green colouring matter can be ex- 

 tracted by alcohol, ether, or oil. The green solution is speedily changed by the action 

 of light in proportion to its intensity, the less refrangible rays of the spectrum acting 

 most actively and rapidly. It then assumes a dirty brownish yellow-green colour, the 

 green colouring matter having become modified or lost its colour. 



If sunlight that has passed through a stratum of the pure green solution not too 

 thick or too dark is decomposed by a prism, an extremely characteristic spectrum is 

 obtained in which rays of very various refrangibility appear to have been more strongly 

 absorbed the darker the solution or the thicker the stratum. This chlorophyll-spectrum 

 has been the subject of much research ; the most recent and comprehensive being that 

 of Kraus, from whose description I borrow the following ^ : — 



The spectrum of an unchanged alcoholic solution of chlorophyll shows seven 

 absorption-bands, four of which are narrow (Fig. 476 A, I, II, III, IF), and are situated 

 in the less refrangible half; while three (F, VI, FII) are broad and are situated in 

 the more refrangible half. The latter, distinguishable as distinct bands only in very 

 dilute solutions, coalesce, even in the solutions of medium concentration which are 

 ordinarily examined, into a single continuous absorption-band occupying the whole of 

 the more refrangible half of the spectrum. 



The bands /, //, ///, and IF are situated in the red, orange, yellow, and yellow-green. 

 The deep black band I, sharply defined on both sides, lies between Fraunhofer's lines 

 jB and C; the three others, shaded off on both sides, diminish in strength in the order of 

 their numbers. Between these bands the illumination is dim, and progressively in the 

 order of the numbers ; /. e. is less dim between II and /// than between / and II, &c. 

 To the left of / the light is undiminished. 



The bands F, FI, and FII in the more refrangible half of the spectrum are shaded 

 on both sides; F\s situated to the right of Fraunhofer's line F', FI, which is dark in the 

 middle, to the left of and on the line G ; FII may be regarded as the total absorption of 

 the violet end. This spectrum has been found in all observations made on the most 

 difl^erent plants ; Mono- and Dicotyledons, Ferns, Mosses, and Algae. 



The Spectrum of liuing leagues agrees with that of the solution in its main character- 

 istics ^ The bands I— Fare, according to Kraus, easily made out in all ordinary leaves 



' Kraus, Sitzungsb. der phys.-med. Soc. in Eriangen, June 7 and July 10, 1871. See also 

 Askenasy, Bot. Zeit. 1867, p. 225 ; Gerland und Rauwenhoff, Archives neerlandaises, vol. VI, 1871 ; 

 and Gerland, Pogg. Ann. 1871, p. 585. [Kraus, Zur Kenntniss der Chlorophyllfaibstoffe u. ihrer 

 Verwandten : Stuttgart, 1872. For reference to Mr. Sorby's papers see Sect, 8 a.] 



^ For further evidence of this very remarkable fact see Gerland und Rauwenhoff, /. c, p. 604. 

 It is not easy to understand how certain physicists can maintain the contrary. [Pringsheim points 



