581.19 177 



III 



The Chemistry of the Forest Leaf 



THE fundamental feature of a leaf is, as everybody knows, the 

 presence therein of a body called chlorophyll, which is defined 

 as " the substance, or maybe a mixture of substances, to which the 

 pure green colour of ordinary healthy leaves and of other vegetable 

 organs is due." Here our attention is at once arrested. Is it pos- 

 sible that no competent and expert chemist can be found who will 

 proclaim with absolute confidence and assurance that chlorophyll is 

 a single substance, or that it is a mixture of substances ? So far as 

 I can find, the original investigator of chlorophyll was Morot, and 

 he gave a hypothetical formula for it, but said it was always 

 accompanied by a fatty substance which he regarded as the 

 cliromogen thereof. In 1860 Eremy showed that the green 

 matter was a simple mixture of two bodies, viz. a blue (phyllo- 

 cyanin) and a yellow (phylloxanthin) existing side by side ; 

 whereas Pringsheim and others held that these were merely de- 

 composition products of an originally single chemical individual. 

 On the other hand, Dr Sorby considered the existence of a chloro- 

 phyll, a phyllocyanin, or a phylloxanthin of a definite chemical 

 composition to be improbable. Meanwhile, an examination of the 

 foliar organs of various species among the great vegetable groups 

 and classes led Gautier in 1866 and later to conclude that chloro- 

 phyll differs among these — nay, even in various species of the same 

 genus it may be dissimilar. But the crowning consummation of 

 all previous researches seems to have been reached in 1895 when 

 Mr Etard, in a memoir read before the French Academy, declared 

 that a given species of plant may contain several chlorophylls, e.g. 

 he describes four distinct, perfectly defined ones as occurring in 

 Lucerne. " It may be concluded," he states, " that the green 

 matters of leaves contain a very stable fundamental nucleus 

 carrying the function of optical absorption in connection with a 

 biological process; and around this nucleus, this trophic point, 

 can be fixed, in a way more or less permanent according to the 

 needs of nutrition, different chemical groupings giving place to 

 chlorophylls different in their composition, their molecular weight, 

 their solubilities, their isomers, and the role which they may play in 

 the living species." "The operations of vegetable synthesis leading at 

 the same time to fatty bodies insoluble in water and to matters emin- 

 ently soluble, always by the intermedium of absorptive green matters, 

 it is natural to think that one and the same chlorophyll would not 

 be sufficient for the work" (Comptcs BenJus, vol. cxx., p. 328). 



x 



