CAROTINOIDS IN THE PHANEROGAMS 43 



may well serve today as our best laboratory outline for working with 

 the class of pigments with which this monograph deals. It was in this 

 paper that Tswett proposed the nomenclature for the carotinoids which 

 has been adopted in this monograph. 



Tswctt's most important contribution to the subject, from an inves- 

 tigational standpoint, was on certain physico-chemical properties of 

 the pigments. He showed (1906b) that the various colored constitu- 

 ents of the chloroplastids, when carefully obtained in certain solvents 

 by methods which avoid the action of plant acids, exhibit very char- 

 acteristic adsorption coefficients towards finely divided materials, such 

 as CaCO :! , inulin and sucrose, as well as many other inert materials 

 which are insoluble in the solvent employed and which can be obtained 

 in a finely divided state. This exceedingly interesting phenomenon 

 is no doubt due to the fact that the various green and yellow chromo- 

 lipoid constituents of the chloroplastids exist in organic solvents in 

 colloidal aggregates of various sizes, the larger colloidal particles 

 being the more strongly adsorbed, and some, like carotin, which is not 

 adsorbed at all, existing in true solution. Tswett found petroleum 

 ether, the carotin solvent, to serve best for the study of these prop- 

 erties, although carbon disulfide was also very useful because of the 

 brilliant color which all the chloroplastid pigments show in this sol- 

 vent, and also because the xanthophylls are especially well differen- 

 tiated in this solvent. This latter fact is no doubt closely related to 

 Schunck's (1903) observations regarding the relative solubility of 

 xanthophylls in carbon disulfide by which he believed he was able to 

 separate them from one another by a shaking-out method. Schunck's 

 observations were near the truth but can not be compared in accuracy 

 with the method of separation which Tswett was able to develop from 

 the colloidal properties of xanthophylls. 



Tswett hit upon a very ingenious method indeed of applying the 

 results of his study. He filtered the moisture-free petroleum ether 

 solution of the mixed chloroplastid pigments for carbon disulfide solu- 

 tion) through a column of perfectly dry CaC0 3 , packed as tightly and 

 evenly as possible in a glass tube, and found that the various pig- 

 ments differentiated themselves according to their adsorption affinity 

 (colloidal aggregation) for the CaC0 3 . The resulting chromatogram 

 (as Tswett proposed to call it) presented a most surprising picture of 

 the chloroplastid pigments, which is strikingly similar in effect, if not 

 in principle, to the well-known Liesegang phenomena. 



By applying this chromatographic method of analysis to petroleum 



