6 3 o SCIENCE PROGRESS 



The effect of fog in London was described by Prof. F. W. 

 Oliver more than twenty years ago and G. Bailey has proved 

 that the same effect can be demonstrated as arising from the 

 aerial conditions in the Manchester district. Glasgow, Birming- 

 ham and Liverpool are other cities that are similarly affected by 

 the smoke evil. 



Nor do these statements rest alone upon the authority 

 of those whom I have mentioned. Cryptogamists in all 

 parts of the British Isles bear testimony from their own 

 observations to the deleterious effect of smoke. A notable 

 instance is the Black Country, which is almost entirely denuded 

 of cryptogams. The smoke-clouds of Yorkshire can be seen at 

 a distance of thirty miles away and their effect is well known. 



The atmosphere itself, apart from its accompanying impurities, 

 has undergone a change which has become particularly marked 

 during the last twenty years, these islands being much drier 

 than formerly. 



One of the causes of the incidence of a drier era is un- 

 doubtedly drainage. We have only to mention the Fens as an 

 illustration of this process being carried out on a large scale to 

 demonstrate the extent to which a limited area in this country 

 has been drained of its inherent moisture but though less obvi- 

 ous elsewhere, drainage has produced a similar effect in all areas 

 brought under the conditions necessitated by modern methods 

 of cultivation. 



The decrease of moisture, which is especially deleterious to 

 hygrophiles adapted to grow only under moist conditions, is 

 indirectly brought about also by the cutting down of trees or 

 woods. Thousands of acres of wood in Scotland, once used as 

 deer forests, have been cut down. In historic times, both England 

 and Ireland were extensively covered by tracts of forest ; 

 remnants of these are to be seen to-day in spots where ancient 

 oaks still linger and are pointed to as the trees under which 

 perhaps Druids once worshipped. Caesar's account of Britain 

 shows that Central England was once a wide region of primaeval 

 forest. To-day, with the exception of isolated forests — Sherwood, 

 Arden, Charnwood l — it is given up to a commonplace mesophytic 

 vegetation and consists largely of pasture or meadow-land. 



Intimately allied to the last factor is the cultivation of land. 



1 Prof. H. Conwentz thought that not a remnant of indigenous woodland could 

 be found in this country. 



