The Yellow Colouring Matters accompanying Chlorophyll. 177 



boundaries in a very curious manner. These pseudo-boundaries are* 

 often polygonal in form, like the real boundaries, and have an intimate 

 geometrical association with them. Under low powers they are in 

 some instances difficult to distinguish from true boundaries ; but the 

 distinction is apparent under high powers, and it becomes obvious as 

 soon as slip-bands are developed by the straining of the metal. The 

 pseudo-boundaries are found to consist in small variations of level 

 in the surface of the grains in which they occur. Their form suggests that 

 they are projections upon the surface of real edges below. They occur 

 very conspicuously in cadmium, especially when it is cast on a cold 

 surface, and less conspicuously in zinc. It is probable that in the 

 strain set up by unequal cooling after the metal has solidified, the lower 

 edges of the crystalline grains project a sort of image of themselves on 

 the surface by slips, or possibly by narrow bands of twinning. The 

 effect resembles that of a Japanese " magic " mirror, in which slight 

 inequalities of the surface, corresponding to a pattern behind, cause' 

 light reflected from the mirror to produce an image in which a ghost of 

 the pattern may be traced. 



The authors regard their experiments as establishing the conclusion 

 briefly stated in their previous paper, to the effect that the plasticity of 

 metals is due to the sliding over one another of the crystalline elements 

 composing each grain, without change in their orientation within each 

 grain, except in so far as such change may occur through twinning. 



" The Yellow Colouring Matters accompanying Chlorophyll, and 

 their Spectroscopic Eelations." By C. A. Schunck. Com- 

 municated by Edward Schunck, F.E.S. Eeceived April 20, 

 — Eead May 18, 1899. 



[Plate 6.] 



The yellow colouring matters dealt with are those accompanying 

 chlorophyll in healthy green leaves and which are extracted along with 

 it by means of boiling alcohol. 



This group of yellow colouring matters is generally known by the 

 name xanthophyll, a term first used by Berzelius, who was the first 

 observer to express the belief that a yellow colouring matter pre-exists 

 along with the green colouring matter in alcoholic extracts of green 

 leaves. The subject has subsequently received the attention of many 

 investigators — Fremy, Michels, Millardet, Miiller, Tinisnaseff, Ger- 

 land, Eaunenhoff, Askenasy, Stokes, Sorby, Tschirch, Kraus, Filhol, 

 Hansen, and Schunck. The principal results arrived at by these 

 investigators are as follows >. — Filhol noticed that by treating crude 

 alcoholic chlorophyll solutions with animal charcoal it is possible to 



