206 Divarf Forms in Barley 



we might perhaps be led to the false conclusion that we were dealing 

 here with the 3 : 1 segregation. In November 1916 seeds taken from 

 9 dwarf and 6 normal plants were sown ; in 1917 all dwarfs were observed 

 to undergo segregation, the offspring from 9 dwarf plants containing 

 altogether 292 dwarfs and 161 normals, i.e. 64*5 and 8.5'5 per .cent, re- 

 spectively, whilst all normal plants were found to breed true to their 

 type. 



From the experiments above stated we see firstly that the normal 

 type is recessive to the dwarf, and secondly that all dwarf plants are of 

 heterozygous constitution. Were the segregation observed in 1916 of 

 the 3 : 1 type, only six out of nine families of dwarfs should be hetero- 

 zygous. Moreover, as the ratio of dwarfs and normals in 1917 is approxi- 

 mately equal to 2 : 1 (= 292:161), it is clear that we are not dealing 

 here with a typical 3 : 1 segregation. 



The experiments of the iwo following years, viz. 1918 and 1919, fully 

 confirm what was said above. Thus all the offspring of dwarf plants 

 underwent segregation into dwarfs and normals in the ratio indicated 



From the above results we see that the ratio of dwarfs and normals 

 is approximately 2:1. On the contrary all offspring derived from normal 

 plants produced only normal plants. 



Furthermore, various crosses were made between the offspring, and 

 also between them and either one of the two original parents, or other 

 normal varieties. The details of these crosses will be omitted here; it 

 will suffice to say that the results corresponded exactly to expectation. 



Ph. De Vilmorin^ has studied the inheritance of dwarf forms in wheat. 

 He obtained two dwarfs against one normal and came to the probable 

 conclusion that such a result might be caused by the fact that any zygote 

 homozygous in respect to dwarfness is either not produced, or, if produced, 

 dies very early. 



Now I have entertained the view that our case, which is very similar 

 to that described by Vilmorin, might be explained by either one of two 

 alternatives below stated, viz. (1) seeds containing zygotes homozygous 

 in respect to dwarfness do not germinate at all, or (2) they die off soon 



1 "Sur une Race de ble naiu infixable.'' Journal of Genetics, Vol. iii. 1913, pp. 67—76. 



