126 



Descriptive and Illustrated Catalogue of the Physiological Series 

 of Comparative Anatomy of the Royal College of Surgeons in 

 London. Vol. iii- Part 1 From the Royal College of Sur- 

 geons in London. 



The following Communications were read : 



1. Observations and Experiments on the Coloured and Co- 

 lourable Matters in the Leaves and Flowers of Plants, 

 particularly in reference to the Principles upon which 

 Acids and Alkalies act in producing Red and Yellow 

 or Green By Dr Hope, V. P. R. S. E., F. R. S. [Con- 

 tinued from 18th Jan.] 



After premising some general remarks respecting the object of 

 research, and enumerating the various authors who had written 

 upon the subject, Dr Hope explained various terms which were to 

 be used in the discourse. To the various coloured matters pre- 

 sented by the leaves and flowers of plants, De Candolle had ap- 

 plied the denomination of Chromule, which term he meant to adopt. 



There resides in the same parts of plants, in addition to the chro- 

 mule, some matter probably destitute of colour, which becomes red 

 by the action of acids, and yellow or green by the action of alka- 

 lies. To it Mr Ellis gave tlie name of colourable matter, which the 

 author changes to Chromogen. When an acid, added to a vegetable 

 infusion, causes a red colour, and an alkali a yellow or green, it has 

 been the universal opinion that both sets of agents act upon one 

 and the same colourable principle. The leading object of this pa- 

 per is to shew that the Clu-omogen, or colourable principle, is not 

 an individual substance ; and that there are two distinct principles, 

 one which forms the red compound with acids, which he denomi- 

 nates Erythrogen ; and another, which affords a yellow compound 

 with alkalies, which he calls Xanthogen. 



To establish that opinion, Dr Hope made many experiments on 

 the leaves and flowers of plants, with various reagents, principally 

 water, alcohol, acids, and alkalies : and has exhibited the results in 

 the compendious form of tables. The first table presents the result 

 of experiments on the leaves of many plants ; and the general result 

 from them, in regard to the special object of inquiry, is, that in ad- 

 dition to the green Chromule, denominated Chlorophyle by many 

 writers, they all contain Xanthogen, and that none of them, except- 



