442 



Mr. II. .0. Sorby on 



[June 1 9^ 



Plate VI. 



This Plate gives various very beautiful transformations of the circular solar spectra 

 as seen by viewing the solar disk of the mercurial globule portrayed obliquely on the 

 stage, which vary in their forms according as the glasses are under- or overcorrected, aa 

 depicted in the figures, which it is needless here to describe in detail. 

 Fig. 34 is another form of mercurial globule, beautifully defined. 



The figures displayed by the magnified artificial star for oblique reflection render it 

 probable that the obliquely illuminated mercury globule, viewed directly in close 

 proximity to the front glass of the microscope upon the stage, is a very imperfect test ; 

 and the methods here described are submitted as possessing very superior delicacy and 

 convenience. 



XXII. " On Comparative Vegetable Chromatology." By H. C. 

 Sorby, F.R.S. &c. Received June 9, 1873. 



TABLE OF CONTENTS. 



Page ! 



Introduction 442 



The absorption-band-raising power 



of solvents 443 



Separation of colouring-matters by 



chemical means 444 



Photochemical analysis ... 445 



"General action of light 447 



Sensitizers 447 



Correlation of optical and chemical 



characters 447 



Comparative quantitative analysis ... 449 



[Fundamental colouring-matters 449 



Description of the groups of colour- 

 ing-matters 450 



Stokes's researches 451 



Chlorophyll group 452 



Blue chlorophyll 452 



Yellow chlorophyll 452 



Chlorofucine , 454 



Spectra of the chlorophyll group 



compared ... 455 



Fluorescence of the chlorophyll group 455 

 Action of acids on the chlorophyll 



gro ip . e 456 I 



Xanthophy 11 group 456 



Phycoxanthine 457 



Peziza xanthine 457 j 



Orange xanthophyll 457 



Xanthophyll 458 



Yellow xanthophyll 459 



General relations of the xanthophyll 



group 459 



Spectra of the xanthophyll group 



compared 460 



Action of light on the xanthophyll 



group 460 



Fucoxanthine 461 



Page 



Lichnoxanthine group 462 



Orange lichnoxanthine 463 



Lichnoxanthine 463 



Yellow lichnoxanthine 464 



Phycocyan group 464 



Phycoerythrine group 464 



Erythrophyll group 464 



Chrysotannin group 465 



Comparative chromatology 465 



Comparison of the same plants grow- 

 ing in different conditions 466 



Action of light on chlorophyll 466 



Production of red leaves 467 



Waste and supply of the colouring- 

 matters in plants 468 



Various comparative quantitative 



analyses 469 



Change in equilibrium due to the 



action of light 471 



Changes in Teltigera canina 471 



Comparison of different plants 473 



Connexion of the different groups of 



Alga 473 



Connexion between the lowest classes 



of animals and plants 474 



Changes occurring in Oscittatorice ... 47 5 

 General connexion of different classes 



of plants 477 



Relation of fungi to other plants ... 478 

 Connexion between the colouring- 

 matters of flowers and those in the 



leaves 478 



Effects of light on flowers 479 



Connexion between fungi and lichens 479 



Yellow varieties of leaves 480 



Condition of chlorophyll in leaves . . . 482 

 Conclusion 483 



Introduction. 



The study of colouring-matters as described in the following paper 

 requires the use of a somewhat special kind of chemistry and of spectro- 



