i on 



Moss : Changes in the Halifax Flora, 



moorlands and then mingling with the West Riding smoke.' 

 • Examples of ' black rain ' at considerable distances from 



large towns are well known.' So high an authority on the 

 subject as Dr. Cohen [13] emphasises the fact that this threat 

 smoke cloud lessens the amount of bright sunshine and reduces 

 the temperature, even at some distance from the towns. It was 

 not stated in June that the influence of smoke on moorland 



vegetation was more than subsidiary; but it is and I have 



studied the question on the spot more than a 'dummy enemy.' 



It is no doubt easy to exaggerate the influence of the firing 

 of the moors : it would appear no more difficult to minimise the 

 same. Keepers from Scotland and from Yorkshire assert that 

 firing increases the heather and bilberry, and keeps down 

 grasses and sedg"es. A well-burnt moor consists almost solely 

 of heather. The late Mr. Robert Smith | 1 1 j —whose loss to 

 British field botany is as regrettable as it is calamitous —also 

 gives the firing- of the moors as one factor in accounting for the 

 increase of heather and for the disappearance of rare moorland 

 plants. This factor was not stated in June to be more than 

 secondary in importance. It is not easy for anyone to faithfully 

 describe a district with which he is personally unfamiliar ; and 

 a detailed botanical survey of the south-west Yorkshire moors 

 shows me that the attempted description of them in August [9J as 

 'occupied by millions of well-rooted Callunas and Vacciniums' is 

 inapplicable to more than half of these extensive tracts. Over 

 the bulk of the Halifax moors these ' millions of well-rooted 

 Callunas ' are conspicuous by their absence ; and the ' millions 

 of well-rooted Vacciniums' are decidedly dwarfed and com- 

 paratively scarce ! ! 



It is difficult to express any opinion on the general question, 

 as the position sketched in February is not the one stated in 

 August. In February [7] we were informed that ' as some species 

 die out naturally, others, as naturally, take their forerunners' 

 place ' ; and the occurrence of CEnanthe crocata at Adel was 

 given as a case in point, it being- looked upon as a supposititious 

 substitution of CE. fistulosa. We were informed in February 

 that 'the natural stay of species may be long- or short,' the 

 supposititious stay of CE. fistulosa at Adel being- the chosen illus- 

 tration ! I admitted in June that there were no doubt exceptional 

 cases of this 'natural short stay,' and positive evidence of authen- 

 ticated cases was asked for, but unfortunately not supplied. In 

 August [9], however, the general position was moved. We were 

 then told that ' as conditions alter, so, slowly, does the flora of 



Naturalist, 



