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Mr. H. C. Sorby on 



[June 19, 



apothecia contain very little, if any, of those substances, but a large 

 amount of the lichnoxanthines so characteristic of the class. Looking 

 upon fungi from this chromatological point of view, they bear something 

 like the same relation to lichens that the petals of a leafless parasitic 

 plant would bear to the foliage of one of normal character — that is to say, 

 they are, as it were, the coloured organs of reproduction of parasitic 

 plants of a type closely approaching that of lichens, which of course is in 

 very close, if not in absolute agreement with the conclusions drawn 

 by botanists from entirely different data. 



Yellow varieties of Leaves. 

 One of the most interesting questions connected with the higher classes 

 of plants is the production of yellow varieties of leaves. Some, instead 

 of being of the usual deep green, are far more yellow, or have special 

 leaves or parts of leaves containing a very little chlorophyll generally 

 diffused. Such leaves must be distinguished from those of normal green 

 character with very bright patches free from chlorophyll, like Croton 

 variegatum. Now I find tbat in many, if not all, such cases there is not 

 only a great change in the total amount, but also a most important 

 difference in the relative quantity of the blue and the yellow chlorophyll . 

 This may be seen by examining the spectra of the leaves themselves, as 

 illuminated by such bright, direct, concentrated sunlight as will penetrate 

 through so many thicknesses of the leaves, pressed together by a strong 

 compressorium, and show the spectrum to advantage. If in this manner, 

 for example, ten thicknesses of very yellow leaves be compared with a 

 single green one, it may be seen that the absorption-bands in the red 

 due to the chlorophylls differ most materially. By proper management 

 the band in the red due to yellow chlorophyll can always be seen in the 

 spectrum of normal green leaves, but no trace is visible in the case of 

 these very yellow leaves — only that due to blue chlorophyll. I have 

 confirmed this conclusion by examining the chlorophyll when in solution 

 in benzole, and find that, though some of the yellow kind is present, the 

 relative amount is much less than normal. The method of study which 

 I have adopted is as follows : — I crush the leaves, and heat them in 

 spirit until all the chlorophyll is dissolved. When cold I agitate with 

 bisulphide of carbon, adding so much water that the whole of the 

 chlorophylls may be carried down ; and after evaporating the bisulphide 

 at a gentle heat, I redissolve in benzole. Taking two tubes containing a 

 solution of such a strength that the spectrum shows the absorption-band 

 in the red of the yellow chlorophyll to the greatest advantage, I add 

 benzole to one tube until the band in the red due to blue chlorophyll is of 

 the same intensity as that due to the yellow chlorophyll in the other 

 tube, as seen by comparing the spectra together side by side with equally 

 bright illumination, and carefully measure how much the original 



