THE BIOLOGICAL CONTROL OF LIFE 39 



pollution of the soil so that the microscopic parasites 

 may not be there to continue the infection. In some 

 mining areas the number of victims has been reduced 

 in twelve years (1902-1914) from 25 to 3, or 22-8 to 1-2 

 per cent., which are eloquent figures. 



One of the striking features of the early years of the 

 twentieth century has been the progress in the experi- 

 mental study of heredity. It received a great stimulus 

 in 1900 with the rediscovery of Mendel's epoch-making 

 investigations, which had been strangely lost sight of 

 since their publication in 1865. A clue has been put 

 into the hands of breeders and cultivators, which has 

 enabled them and will increasingly enable them to 

 contribute to the betterment of man's estate — as far as 

 his domesticated animals and cultivated plants are 

 concerned. From Professor James Wilson's admirable 

 Manual of Mendelism (1916) we take two or three 

 illustrations. 



The average yield of wheat in Britain is about 32 

 bushels to the acre. Professor Wilson tells us that it 

 might be raised to 40 or even 50. " For every day by 

 which the life of a variety of wheat is shortened between 

 seedtime and harvest, the wheat-growing area in Canada 

 reaches fifty or sixty miles farther northwards. A 

 vigorous, early ripening and highly productive oat, 

 together with a turnip having the same characters, 

 might increase the returns from many a northern or 

 high-lying farm in Britain and might even be the means 

 of causing many a pasture field to revert once again 

 to the plough without the artificial and precarious 



