18 NEW I.ICnF.NS FKOM TTTK CAI'F. OF GOOD HorE. 



xanthine — two substances which arc altogether distinct in every rela- 

 tion, both fhcmical, physical, and biological. 



I am fully prepared to admit that by using a sufficient (juantity 

 there would be no difficulty in detecting the chief absori)tion band of 

 chlorophyll in the xanthophylls obtained from leaves, but there is no 

 difficulty in procuring them almost, if not absolutely, free from it by 

 using the petals of suitable flowers. I must confess that I am 

 astonished at the idea of supposing that substances giving spectra with 

 all the characters which would be due to variable mixtures are 

 separate compounds. If such a system were adopted, the whole sub- 

 ject of colouring matters would be so confused as to break down 

 altogether. The principle wliich I have always adopted has been 

 never to look upon any spectrum as evidence of a new and separate 

 substance when it could be perfectly well explained by supposing it to 

 be due to a mixture of previously recognised substances, certainly 

 met with in an isolated or isolatable condition in closely related 

 natural products. Pringsheim fully admits that the bands in some of 

 the yellow substances he describes correspond exactly with those of 

 chlorophyll. Every fact can be completely explained by supposing 

 that this substance could not be completely separated by the method 

 employed. There is no kind of doubt that the extent to which such 

 separation can be eflPccted depends on a variety of conditions still very 

 imperfectly understood ; and if we were to suppose that when we 

 cannot sejiaratc colouring matters from one another there was evidence 

 of some new and independent substance, their number would be all 

 but infinite. Such minute quantities of chlorophyll may be detected 

 by the remarkably dark band in the red, that we may almost look upon 

 it as being like the sodium band in the case of incandescent vapours. 

 I must say that I regard some of Pringheim's conclusions much in the 

 same light as if anyone studying the spectrum of potassium and 

 finding that it showed the bright yellow lines of sodium, were to con- 

 clude that he had discovered a new element forming a connecting link 

 between potassium and sodium. 



In conclusion, I must also say, that I am astonished that so few 

 have hitherto observed the very complete proof of the normal 

 chlorophyll of many plants being a mixture of two entirely different 

 kinds. There is often no difficulty in seeing the characteristic bands 

 of both in the spectrum of the living plants, especially in sucli green 

 Alga3 as Ulva, and yet, with the exception of Prof. Stokes,* no one 

 seems to have observed the facts or appreciated their iniportauce. 



NEW LICHENS FROM THE CAPE OF GOOD HOPE. 

 Br THE Rev. J. M. Ckomdie, F.L.S. 



Amokqst the Lichens collected by the Rev. A.. E. Eaton on Table 

 Mountain, during the short stay of the Venus Transit Expedition at 

 the Cape, there occur various novelties, which Dr. Nylaiider has 



* Proceed. R. S , 18G4, xiii., p. 114. 



