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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



to determine the nature of the substance to which the brown 

 colour of the leaves after treatment with alcohol is due, but I 

 had not much success. The substance, whatever it is, is nearly 

 insoluble in the usual menstrua — alcohol, ether, chloroform, 

 acetic acid, &c. ; it dissolves partly in caustic lye, but entirely 

 and easily in cone, sulphuric acid, forming a dark brown solution 

 from which it is precipitated by water in brown flocks. What 

 it is I cannot say, but its formation under the circumstances con- 

 firms me in the suspicion I have long entertained, that the 

 effect produced by fog on green leaves is not always and entirely 

 due to acids, as has been supposed." 



The next quotation, from the same source, refers to samples 

 of leaves in which I had microscopically detected what I had 

 assumed to be " chlorophyllan." Concerning these Dr. Schunck 

 says : " I have examined the leaves as well as I could, and I find 

 that they are very similar inter sc so far as regards the cause of 

 their discoloration, but differ in this respect from the leaves 

 previously sent, inasmuch as the colouring matter contained in 

 them must have been altered by the action of acid in some form 

 or other. The big leaves of Bhccdia do indeed contain, as you 

 suppose, what may for convenience sake be called chlorophyllan 

 (though this is, in my opinion, a mixture of substances), i.e. a 

 product of the action of acids on chlorophyll, and the brown 

 granules, of which you make mention, may indeed be this 

 product. 



" It would, however (so I think), be a mistake to suppose that 

 the formation of this product was entirely due to the action of 

 some deleterious matter outside the plant. All green leaves, or 

 nearly all, turn more or less olive-coloured on standing or lying, 

 and their alcoholic or other extracts do the same in conse- 

 quence of the action of the acid pre-existing in the leaves, or 

 which is formed on exposure of the extracts to air, on the chloro- 

 phyll ; but, of course, this action may be hastened by anything 

 that destroys the vitality of the leaf and allows the chlorophyll 

 to come into contact with other cell-contents. 



" The alcoholic extracts of the leaf of Schlcgclia and of the 

 Begonia do not differ from that of liheedia ; but in the case of 

 SchlegeHa I think I see evidence of the action of something 

 besides acid, insomuch as the leaf after extraction with boiling 

 alcohol retained a distinct brown coloration." 



