IX 



SIMILAR EFFECTS 



In the last chapter, a case in which two different factors 

 produced a similar effect was discussed. In this, we 

 shall discuss two others. During the last quarter of a 

 century an enormous amount of work in the production 

 of new varieties of plants has been done at the seed- 

 breeding station at Svalof in Southern Sweden. Since 

 the discovery of Mendel's papers, this work has vastly 

 increased both in quantity and precision, and no section 

 has been more successful than that now under the care 

 of Professor Nilsson-Ehle which has to do with the 

 production of new varieties of oats and wheat. Professor 

 Nilsson-Ehle has published many papers, but the results 

 with which we have to deal are to be found in two papers 

 " Kreutzunguntersuchungen an Hafer und Weizen " 

 (" Crossing Experiments with Oats and Wheat ") 

 published by the University of Lund in 1909 and 1911. 

 Among oats there are five or six chief colours of 

 grain, namely, black, brown, tawny, grey, yellow, and 

 white, but some are slightly indefinite. It would be 

 difficult to say that there is either an absolutely black 

 or an absolutely white grain. What is generally under- 

 stood by " black " is a very dark brown, like dark 

 chestnut or dark oak, and by " white " a more or less 

 faded cream or dull white. Besides, there are shades 



in 



