ECONOMIC 147 



field to revert once again to the plough without the 

 artificial and precarious stimulus of a protective duty. 



But how are these new varieties to be produced ? 

 The way has been already shown by such workers as 

 Patrick Shirreff and the staff at Svalof in Sweden. There 

 were other raisers of new varieties before Shirreff, but 

 none so long persistent and none whose work illustrates 

 better what can and what cannot be done without 

 Mendel's law. Shirreff tells us how he began to raise 

 new varieties on his farm in East Lothian : " When 

 walking over a field of wheat on the farm of Mungoswells, 

 in the county of Haddington, in the spring of 1819, a 

 green, spreading plant attracted my notice, the crop 

 then looking miserable from the effects of a severe 

 winter ; and next day measures were taken to invigorate 

 its growth by removing the surrounding vegetation and 

 supplying manure to the roots. In the course of the 

 summer several stalks were cut down by hares ; but, 

 notwithstanding this loss to the plant, sixty-three ears 

 were gathered from it at harvest, yielding 2473 grains, 

 which were dibbled in the following autumn at wide 

 intervals. For the two succeeding seasons the accu- 

 mulating produce was sown broadcast, and the fourth 

 harvest of the original plant amounted to about 42 qr. 

 of grain fit for seed ; and proving to be a new variety, 

 it was named Mungoswells wheat." 



For thirty years Shirreff persisted in this work of 

 selecting single plants in his own and his neighbours' 

 fields and testing and accumulating stocks till he had 

 given the world a large number of new varieties. Then 

 came the tragedy. He began crossing, and, as we 

 should now expect, his crosses did not breed true but 

 were so variable that he became bewildered in the 



