October 20, 192 1] 



NATURE 



245 



overwhelming majority of people arrive at the 

 grave, however, without having had the slightest 

 conception of the dehcate chemical machinery and 

 the subtle physical changes which, throughout 

 each moment of life, they have methodically and 

 unwittingly operated. 



Chlorophyll and Haemoglohin. 



To those who delight in tracing unity among 

 the bewildering intricacies of natural processes, 

 and by patient comparison of superficially dis- 

 similar materials triumphantly to reveal continuity 

 in the discontinuous, there is encouragement to be 

 found in the relationship between chlorophyll and 

 hcemoglobin. Even the most detached and cynical 

 observer of human failings must glow with a sense 

 of worship when he perceives this relationship, and 

 thus brings himself to acknowledge the com- 

 monest of green plants among his kindred. Be- 

 cause, just as every moment of his existence 

 depends upon the successful performance of its 

 chemical duties by the haemoglobin of his blood 

 corpuscles, so the life and growth of green plants 

 hinge on the transformations of chlorophyll. The 

 persevering elucidation of chlorophyll structure 

 ranks high in the achievements of modern organic 

 chemistry, and in its later stages is due principally 

 to Willstatter and his collaborators, whose in- 

 vestigations culminated in 1913' 



This is not an occasion to follow, otherwise 

 than in the barest outline, the course of labora- 

 tory disintegration to which the chlorophyll mole- 

 cules have been subjected by the controlled attack 

 of alkalis and acids. The former agents reveal 

 chlorophyll in the twofold character of a lactam 

 and a dicarboxylic ester of methyl alcohol and 

 phytol, an unsaturated primary alcohol, 

 C20H39.OH, of which the constitution remains 

 obscure in spite of detailed investigation of its 

 derivatives ; but the residual complex, represent- 

 ing two-thirds of the original molecule, has been 

 carefully dissected. The various forms of this 

 residual complex, when produced by the action of 

 alkalis on chlorophyll, have been called " phyll- 

 ins " ; they are carboxylic acids of nitrogenous 

 ring-systems, which retain magnesium in direct 

 combination with nitrogen. The p>orphyrins are 

 the corresponding products arising by the action 

 of acids ; they are carboxylic acids of the same 

 nitrogenous ring-systems from which the mag- 

 nesium has been removed. The phyllins and the 

 porphyrins have alike been degraded to the 

 crystalline base, setioporphyrin, into the composi- 

 tion of which four variously substituted pyrrole 

 rings enter. It is this assemblage of substituted 

 pyrroles which, according to present knowledge, 

 is the basic principle also of the blood-pigment, 

 in which iron plays the part of magnesium in 

 chlorophyll. 



Anthocyans, the Pigments of Blossoms and 

 Fruits. 



Since the days of Eden, gardens have main- 

 tained and extended their silent appeal to the 

 more gentle emotions of mankind. The subject 

 NO. 2712, VOL. 108] 



possesses a literature, technical, philosophical, 

 and romantic, at least as voluminous as that sur- 

 rounding any other industrial art, and the am- 

 bition to cultivate a patch of soil has attracted 

 untold millions of human beings. Amongst 

 manual workers none maintains a standard of 

 orderly procedure and patient industry higher 

 than that of the gardener. Kew and La Mortola 

 defy the power of word-painters to condense their 

 soothing beauty into adequate language, whilst 

 that wonderful triangle of cultivation which has 

 its apex at Grasse almost might be described as 

 industry with a halo. 



Prior to 191 3 the most fruitful attempt to isolate 

 a colouring-matter from blossoms in quantity 

 sufficient for detailed examination had been made 

 by Grafe (1911), but the conclusions to which it 

 led were inaccurate.' In the year mentioned, how- 

 ever, Willstatter began to publish with numerous 

 collaborators a series of investigations, extend- 

 ing over the next three years, which have brought 

 the subject within the realm of systematic chem- 

 istry. For the purpose of distinguishing gluco- 

 sidic and non-glucosidic anthocyans the names 

 anthocyanin and anthocyanidin respectively were 

 applied. The experimental separation of antho- 

 cyanins from anthocyanidins was effected by par- 

 tition between amyl alcohol and dilute mineral 

 acid, the latter retaining the diglucosidic antho- 

 cyanins in the form of oxonium salts and leaving 

 the anthocyanidins quantitatively in the amyl 

 alcohol, from which they are not removed by 

 further agitation with dilute acid ; the monogluco- 

 sidic anthocyanins were found in both media, but 

 left the amyl alcohol when offered fresh portions 

 of dilute acid. 



The earliest of these papers, published in con- 

 junction with A. E, Everest, dealt with corn- 

 flower pigments, and indicated that the distinct 

 shades of colour presented by dift'erent parts of 

 the flower are caused bv various derivatives of one 

 substance ; thus the blue form is the potassium 

 derivative of a violet compound which is con- 

 vertible into the red form by oxonium salt-forma- 

 tion with a mineral or plant acid. Moreover, as 

 found in blossoms, the chromogen was observed 

 to be combined with two molecular proportions 

 of glucose and was isolated as crystalline cyanin 

 chloride ; hydrolysis removed the sugar and gave 

 cyanidin chloride, also crA'stalline. Applying these 

 methods more generally, Willstatter and his other 

 collaborators have examined the chromogens 

 which decorate the petals of rose, larkspur, holly- 

 hock, geranium, salvia, chrysanthemum, gladi- 

 olus, ribes, tulip, zinnia, pansy, petunia, poppy, 

 and aster, whilst the fruit-skins of whortleberrv', 

 bilberry, cranberry and cherry, plum, grape, and 

 sloe have also been made to yield the pigment 

 to which their characteristic appearance is due. 



Micro-hiochemistry . 



Amongst the many sources of pleasure to be 

 found in contemplating the wonders of the uni- 

 verse, and denied to those untrained in scientific 



