NILSSON'S DISCOVERY 83 



crosses have been artificially made, the fact that one new 

 character by this means yields a very large number of new 

 varieties is universally known, and one of the most ordin- 



Fig. 24. Svalof oats with spreading branches. 



ary means of producing novelties. Moreover, if one new 

 unit may double the number of the separate types, a second 

 new unit may tend to increase it fourfold, a third eightfold, 

 and so on. From this calculation it mav be seen th^t even 



