36 DR. EDWARD SCHUNCK ON THE 



dogwood. It imparts a dingy hue to the leaves, and is there- 

 fore not much noticed. I observed a case of its occurrence 

 last summer, which I had not previously seen mentioned. 

 Passing through a field of corn, which was then nearly ripe, 

 I saw a number of plants by the sides of the path with 

 blades distinctly purple. On closer observation it was 

 evident that in all cases where this coloration occurred the 

 ears of corn had been cut off before ripening, the act pro- 

 bably of idle passers-by, those plants which remained un- 

 injured having become yellow as usual. I inferred that it 

 was the injury sustained by the plant and the arrest of its 

 main function, that of the development of seed, that had led 

 to the formation of some purple substance, not seen during 

 the process of natural decay. I made some experiments on 

 this purple colouring-matter ; but all I can say about it is, 

 that it belongs to the same class as the red and yellow 

 colouring-matters of faded leaves. I anticipated the pos- 

 sibility of its being identical with a product of the decom- 

 position of chlorophyll, crystallizing in purple needles, 

 which I had discovered in the course of my investigation ; 

 but I was disappointed in my expectation. 



As regards the nature of the colouring-matters to which 

 the various colours of faded leaves are due, opinions vary. 

 It is generally supposed that they are formed from chlo- 

 rophyll by some process of decomposition, probably of oxi- 

 dation ; and nothing can be more natural than this suppo- 

 sition. On exposure of the leaf to light and air, after its 

 vital functions have ceased, the green colour due to chloro- 

 phyll gradually disappears and is succeeded by red, yellow, 

 or purple. Therefore, it is argued, the respective colouring- 

 matters must be derivatives of chlorophyll. Nevertheless 

 this view is open to some objection. As regards, in the 

 first place, the red colouring-matter, since no one has suc- 

 ceeded in obtaining it artificially, it must be formed, if a 



