66 Mendelian Tnheritonce and Yellotv Rust in Wheat 



Rows 43 to 82 (sown February 1918) were examined at two different 

 periods, viz. June 15tli to ITth, and again July I6tli to 29tli. 



By the end of July the plants were beginning to mature, and, after 

 making the final examination of the autumn-sown crop, it was found that 

 the spring-sown portion was too far advanced for another examination 

 to be made. In each case the final examination was made only a few 

 days previous to the ripening of the plants. 



Tabiu 1 1. Rcmillx from, fjradiiu/ the Fn plants ( l'.)18) ucroyiling to t/ir erlent 

 of the rtiKl. attack. (Cross No. 120.) 



Totals l.'>()0 347 107 391 294 200 155 



The final condition of the F.^ generation is shown by Tal)]!' II. Of 

 829 plants in the autumn-sown portion, 202 remained rust-free through- 

 out the season, while the remaining (i27 plants showed evidence of more 

 or less susceptibility. This is a close approximation to the 3 : 1 Mendelian 

 ratio. 



In the spring-sown portion, it will be obsen^ed, the proportion of 

 completely rust-free individuals was considerably less tiian one-fourth 

 of the total number, but, on the other hand, the proportion of plants 

 bearing only traces of rust was much higher than in the autumn-sown 

 crop. 



The whole F^ generation contained 1213 rusted and 347 rust-free in- 

 dividuals. If the badly rusted plants (giades 3 and 4) be separated from 

 those that wei(( lijss severely attacked, we obtain the following totals: 



Attack, bad to very severe 361 plants 

 Attack, moderate or less 852 plants 

 Entirely free from rust 347 plants 



While these figures do not show a very rlose approximation to the 

 simple Mendelian ratio, they are certaiidy very suggestive of it. Fuither 

 consideration of these figures is deferred until the later results have been 

 given. 



