ON THE EFFECTS OF URBAN FOG UPON CULTIVATED PLANTS. 33 



siderable number of plants has been carefully followed, but for the 

 purposes of this report I do not think it desirable to enter very 

 fully into the matter. Moreover, our experiments are by no means 

 ■concluded. My impression is that the action of phenol is entirely 

 parallel to that of aniline, which has been fully investigated by 

 Dr. Schunck in conjunction with Brebner.* With phenol, as 

 with aniline, a dark brown substance is formed in the protoplasm 

 of living tissues of many plants. Different plants, in both cases, 

 vary in the degree in which they react with the poisons, Mono- 

 cotyledons in general giving a less complete alteration of colour 

 than Dicotyledons. Schunck and Brebner concluded that the 

 aniline was oxidised by some form of " active oxygen " present 

 in the protoplasm, and, so far as my experiments have gone, I 

 am of the same opinion in regard to phenol. This substance has 

 no action upon dead tissues, nor has it upon the leaves of plants 

 which have been kept in an atmosphere of pure hydrogen until 

 the evolution of carbonic acid ceased. With hydrogen peroxide, 

 phenol gives a dark brown precipitate if a little ferric sulphate 

 be present to aid the reaction. 



Although in some cases the chlorophyll-corpuscles turn 

 partially or completely brown with phenol, this is by no means 

 universal. Even where the brown colour is produced I doubt if 

 the chlorophyll has much part in the reaction. The marked 

 change in colour in the corpuscles does not necessarily denote 

 that the pigment has been destroyed. The corpuscles are centres 

 of great chemical activity, and may well contain active oxygen. 

 I am indebted to Dr. Schunck for the information that an 

 alcoholic extract of pure chlorophyll exhibits no noticeable 

 change in regard to its absorption spectrum when treated with 

 phenol. I further find that alcoholic extracts of leaves dis- 

 coloured by phenol give spectroscopic evidence of the presence of 

 pure chlorophyll. Though hardly entitled to express an opinion 

 on this subject, I feel pretty sure that the chlorophyll is only 

 masked by the brown colouring matter, and that it takes no 

 direct part in its production. 



It should be added that we find naphthalene, benzene, and 



unaltered, the pigment in every respect resembling that of uninjured leaves. 

 The production of these granules has a distinct bearing on a recent dis- 

 cussion upon the so-called " proteosomes." With the assistance of Miss 

 Ewart, I hope to deal with this question in extenso in another place. 

 * Annals of Botany, vol. vi. p. 167. 



D 



