2go Kelerate. 



Nilsson-Ehle, H.,^ Kreuzungsuntersuchungen an Hafer und Weizen. Lunds 



Universitets Arsskrilt. N. F. Afd. 2. Bd. 5, Nr. 2 1909, S. i — 122. 



This remarkable contribution to genetics clears up several unsettled 

 points in Medelian inheritance. It points a way to the interpretation of 

 an even broader field of phenomena than the author has discussed. 



The writer began his investigations at the plant breeding station 

 "Sveriges Utsädesförening" at Svalöf in 1900, and his conclusions, there- 

 fore, are supported by a large amount of data. Critics may object that 

 he is too ardent a Mendelian to give a perfectly fair interpretation of his 

 facts, but one can hardly fail to agree with him that all the characters 

 of wheat and oats that he has had under observation are better interpreted 

 by Mendelian formulae than by anything else yet proposed. 



The fact that all these characters are MendeUan in their inheritance 

 is not so important, however, as is one particular class of his facts. He 

 shows conclusively that more than one Mendelian pair exist, each of which 

 is the same potential character. For example, in most of his crosses be- 

 tween presence and absence of black in the glumes of oats, the character 

 was transmitted as a simple Mendelian mono-hybrid; yet in one case there 

 were two definite independent allelomorphic pairs in each of which pre- 

 sence of black was dominant to absence of black. If these blacks are 

 represented by the letters Bi and B2, and a black-glumed variety 6162 is 

 crossed with a white-glumed varietj' bjbs, in the F, generation there will 

 appear 15 black-glumed plants to one white-glumed plant. Furthermore, 

 a black-glumed plant Bib» may be crossed with a black-glumed plant biB-, 

 and the same result obtained. This seems to be a logical explanation of 

 many cases of reversion in commercial plant breeding when two varieties 

 apparently pure for a certain character are crossed and in the F» generation 

 the absence of that character appears. 



In wheat he found three independent allelomorphs for presence of red 

 color in the seed coat of a very old red variety from the north of Sweden. 

 In all other red varieties the color was due to only one pair. When the 

 three independent allelomorphs were present, the theoretical expectation 

 of the F3 generation as proved by the crops of the Fo generation, should 

 be 37 constant red, 8 segregating reds and whites in the ratio 63 : i, 

 12 segregating and reds whites in the ratio 15 : i, 6 segregating reds and 

 whites in the ratio 3 : i and i constant white, out of a total of 64 plants. 

 What he actually obtained was 50 constant red, 5 segregating 63 : i, 

 15 segregating 15 : i, 8 segregating 3 : i and o constant whites out of 78 

 plants of the F-z generation. It was unfortunate that he did not obtain 

 the expected pure white, but this might well happen when dealing with 

 such a small number. 



In still another case, he found that instead of behaving as a mono- 

 hybrid — the usual manner — presence of ligule in one variety of oats 

 needed four independent allelomorphs to account for the ratios obtained in 

 the F3 generation. Of course where one is dealing with four characters 

 and only one pure recessive is expected in 256 plants, the field results 

 are necessarily difficult to analyze. This case cannot be said to have been 

 definitely proved, but in the other two instances there can be no doubt 

 about tlie facts. 



The reviewer has independenth' obtained similar facts in maize, and 

 granting their frequent occurrence it can be shown that here there is a 

 logical interpretation of many cases where variation is apparently conti- 

 nuous. Further, if in certain cases the character pairs are cumulative in 



