J. W. H. Harrison 233 



tive of what has happened elsewhere. Much the same holds true of 

 Moray Firth Triphaena comes^. 



(2) Both in winter and summer I have made prolonged critical 

 examinations concerning the colouration of the bark of the trees in 

 Middlesbrough Park, in which vicinity more soot is produced and carried 

 down to vegetation than in any other locality I have worked. I con- 

 fidently assert that, except when jutting branches deliberately shut off 

 the action of the rain, the trunks are not significantly different in tone 

 from those in the rural districts of Durham and Yorkshire far removed 

 from urban influence. The Scotch firs remained reddish grey, the white 

 poplars greenish grey, the birches silvery, the ashes ashen and so on. 

 The same is correct too of trees growing in the Team valley, North 

 Durham, within the smoke zone not only of the local works of Birtley 

 but of Newcastle and Gateshead, and in the Team valley melanism of a 

 most aggressive type affecting hosts of species is rampant. To gain 

 some kind of appreciation of the condition of tree trunks in the latter 

 neighbourhood at night time, on March 9th, 1919, a starlight night with 

 moon somewhat obscured, I walked down the valley from Birtley 

 towards Gateshead and studied the trees. Their paleness was so much 

 exaggerated that I found myself classifying pale sycamore trunks as 

 silver birches until nearer approach revealed the specialised buds and 

 twigs of the sycamore. 



(3) In damp districts I deny that the effect of heavy rainfall is to 

 blacken either rock faces or tree trunks. In my experience, gained in 

 the west of Durham and Northumberland (rainfall 44 inches), in Ireland 

 and in Scotland the moisture favours the development of algae, lichens 

 and bryophytes which are far from being black in hue ; in many cases 

 the rocks become bright in colour owing to the presence of such highly 

 coloured lichens as the very common bright orange Physaia parietina. 



(4) Another fatal objection seems to lie in the fact that only 

 insects resting in such blackened positions should be capable of assuming 

 a melanic guise under the action of natural selection. This is not the 

 case, and examples illustrative of the point are easy to obtain. For 

 instance, Larentia multistrigaria (except very rarely) rests by day on 

 the sheltered side of tufts of Nardtbs stricta amongst which its food- 



^ Tutt says that this has arisen by natural selection working on an insect resting on 

 peat ; my only objection is that it can't ! Probably no worker save myself has ever 

 had a dozen examples of the Moray Firth insect captured at rest by day ; without excep- 

 tion these were taken from grass tufts and not from bare soil of any kind — peat or 

 otherwise. 



