uSo GENERAL CONDITIONS OF PLANT-LIFE. 



If an alcoholic solution of chlorophyll (according to Conrad it must be very dilute^) 

 is agitated with any quantity of benzol (say double its volume) two very sharply 

 separated strata are formed after the fluid comes to rest, a lower alcoholic stratum 

 of a pure yellow colour, and an upper blue-green stratum of benzol. Kraus considers 

 this process to be a dialytic one ; there are, according to him, two colouring substances 

 in the ordinary chlorophyll-solution, a blue-green and a yellow one, soluble in very 

 different degrees in alcohol and benzol^. 



Kraus therefore holds the spectrum of chlorophyll to be a combination-spectrum, 

 i. e. that it arises from the superposition of the two spectra of the blue-green and 

 the yellow colouring-matter. The blue-green substance gives the four narrow 

 absorption-bands in the less refrangible half of the spectrum (Fig. 447, B), and part 

 of the band VI which is situated at G in the more refrangible half. The band F 

 (Fig. 447 C) results from the yellow colouring matter which has absorption-bands 

 in the more refrangible half of the spectrum. The band VI of the chlorophyll-spectrum 

 is the result of partial superposition of corresponding bands in the spectra of the 

 yellow and the blue-green substances, which however do not perfectly coincide. Both 

 colouring substances alike produce the absorption-band VII at the violet end. 



The yellow colouring m.atter is soluble in alcohol, ether, and chloroform, but not 

 in water. On addition of hydrochloric or sulphuric acid (as Micheli had already 5hown) 

 it becomes first emerald-green, then verdigris-green, and finally indigo-blue; the 

 spectrum of the yellow substance which has in this manner become gi-een shows 

 altogether different absorption-phenomena to those of chlorophyll. The spectrum of 

 the yellow ingredient of chlorophyll is identical with that of most yellow flowers (as 

 Ranunculus, Mimulus, Gentiana lutea, Brassica, Taraxacum, Matricaria, &c.), and agrees 

 with it also in the reactions just named, as also does that of the yellow colouring 

 substance of fruits and seeds (Euonymus, Solanum, Pseudocapsicum &c.) ; this yellow 

 substance is, like chlorophyll, combined with protoplasm. The substance present in 

 the cells in the liquid form, as for instance in the flowers of the dahlia, is different ; 

 it is soluble in water, and does not give a spectrum consisting of bands, but a continuous 

 absorption of the blue and the violet. The colouring substance of some orange flowers, 

 e.g. Eschscholtzia, also soluble in alcohol, is again different, possessing a fourth band 

 in the blue-green to the left of the three bands of the ordinary yellow substance. The 

 colouring matters of bright-coloured lower organisms which are soluble in alcohol are 

 not identical with either of the two which constitute chlorophyll, but are related to them. 



According to Kraus, the yellow substance of etiolated leaves also exactly resembles 

 the yellow constituent of chlorophyll; he considers the green colour produced by 

 exposure to light to be the result of the formation of the blue-green constituent. 



The Fluorescence of the colouring-matter of chlorophyll is seen from the fact that 

 a sufficiently dark concentrated solution appears dark-red by reflected but green by 

 transmitted light. The fluorescence is much more decided if the pencil of converging 

 rays of the sun is made to fall on the green fluid through a condensing lens. If the 

 solar spectrum is thrown upon the surface of a solution of chlorophyll^, it may be 



^ Kraus obtained a solution of chlorophyll by pouring alcohol upon boiled leaves which have 

 contained water. Conrad shows that it is only such dilute solutions of chlorophyll (alcohol of 

 65 p. c. or less) that show Kraus's reactions ; and that on the contrary a solution obtained from 

 dried leaves by absolute alcohol and then mixed with benzol does not separate into yellow and 

 blue-green strata. 



^ This is however rendered doubtful by Conrad's more recent researches. If a solution of 

 chlorophyll in absolute alcohol is evaporated, the residue extracted with water does not contain 

 a yellow constituent as it does when the solution is prepared with dilute alcohol. It is therefore 

 not improbable that chlorophyll-green is decomposed by dilute alcohol, and that the two con- 

 stituents of which Kraus supposes chlorophyll to consist did not exist before the operation an) more 

 than those imagined by Fremy. 



•■ Hagenbach, Pogg. Ann. vol. 141, p. 245; Lommel, ih. vol. 143, p. 571. 



