464 



Mr. H. C.-Sorby on 



[June 19, 



Yello i v Lich } wssa nthine. 



I have adopted this name for a substance very similar to that just 

 described, but giving a spectrum in which the absorption does not ex- 

 tend so far from the blue end, so that the colour is a more pure yellow. 

 It is best obtained from Parmelia (Physcia) parietina by the same pro- 

 cess as that just described. 



Phycocyan Group. 



I have described the two principal species of this group in former 

 papers*, and will therefore only briefly allude to a few characters. 

 Phycocyan gives a spectrum with a well-marked absorption-band in the 

 orange, and has a very intense red fluorescence, due to a narrow red 

 band. Pink phycocyan gives a similar kind of spectrum, only the principal 

 absorption-band lies between the yellow and the green. It, too, is highly 

 fluorescent, but the light of fluorescence is orange, due to a much 

 broader band. These two mixed together constitute Cohn's phycocyan. 

 Both are soluble in water, but exist in the plants in a solid form or con- 

 centrated solution, as shown by the position of the absorption-bands, 

 which lie considerably nearer to the red end than when the corre- 

 sponding substances are dissolved in water. 



Phycoerythrine Group. 



This is the name I propose to adopt for two colouring-matters found in 

 Algce, described by me in a former paper f. One is pink, giving a spec- 

 trum with an absorption-band at the yellow end of the green, and the 

 other is red, the spectrum showing a band at the blue end of the green. 

 I therefore call one pink phycoerythrine and the other red phycoerythrine. 

 Neither are fluorescent, and both are soluble in water. 



Erythrophyll Group. 



This is the name I have applied to a large number of colouring-matters, 

 soluble in water and insoluble in bisulphide of carbon, found in the leaves 

 and petals of plants. I shall not now attempt to describe them in detail, 

 but refer to my former papers for a further but yet very imperfect ac- 

 count of their peculiarities:?:. They do not appear to be essential con- 

 stituents of leaves, but rather products formed under particular conditions. 

 Much remains to be learned respecting the different kinds ; for though 

 an accidental constituent, there are important differences between those 

 formed under similar circumstances in the leaves or fronds of different 



* Monthly Microscopical Journal, 1870, vol. iii. p. 229, and 1871, vol. vi. p. 124. 

 t Monthly Microscopical Journal, 1871, vol. vi. p. 124. 



\ Proc. Eoy. Soc. 1867, vol. xv. p. 433. Quart. Journ. of Science, 1871, vol. i. p. 64. 

 Quart. Journ. of Microscop. Science, 1871, vol. xi. p. 215. 



