YIELDING CAPACITY OF WHEAT 171 



with regard to the factors which determine the 

 yield per acre. Many play their part in deter- 

 mining it, the master factor of the whole set 

 probably being the available water supply during 

 the period of most rapid growth in May and June. 

 If this is suitable then soils usually considered 

 unsuitable for wheat cultivation can carry crops 

 well up to the general average of the country. 

 Apart from this, however, yield is largely a matter 

 of variety, for on the same field one variety may 

 consistently give greater crops than another. 

 Whether the capacities for giving large or small 

 yields are hereditary or not has so far proved 

 incapable of analysis. There is evidence that such 

 segregation can occur, for high and low yielding 

 varieties have been isolated from the same cross 

 when there has been an appreciable difference in 

 these respects in the parents. But to estimate 

 the proportions of the two forms in the F 2 genera- 

 tions is impossible, for no inspection of a single 

 plant can reveal its cropping capacity per acre. 

 In handling crosses between low-yielding strong 

 wheats and heavy-yielding weak wheats much has 

 to be left to chance. One simply picks out the 

 types one considers suitable and then after rejecting 

 those which are obviously deficient in strength 

 propagates them with a view to determining their 

 cropping capacity as opportunity offers. For 

 selecting in this fashion it is essential that the plants 

 of the F 2 generation should be grown under the 



