Growth and variation in maize. 165 



here although many others showing the same thing can be found. 

 These plants are taken from series A table 13. 



Plant No 44 45 46 47 48 49 



Mean Qiiintile Position 4-50 2-28 1-71 4-64 I'SO 4-21 



Here within a distance of some seven feet there are three very 

 small plants and three very large ones. It is improbable that the 

 difference in the soil or other conditions could account for the gi-eat 

 difference between plant No. 48 and those standing eighteen inches to 

 either side of it. Many other examples showing the same thing could 

 be picked out of these tables. 



It, therefore, is highly improbable that the differences in the 

 growth of individual plants are to be accounted for on the basis of 

 environmental factors. 



At several places in this paper occasion has been taken to point 

 out that the facts could be interpreted by assuming that gi'owth is 

 controlled by internal factors. Within the past few years it has been 

 clearly shown by Xilsson-Ehle, East and Hayes, Emerson and East and 

 others that the inheritance of quantitative characters may be explained 

 upon a Mendelian factor basis. Thus Emerson and East (:13) present 

 a considerable amount of evidence to show that the height of corn 

 plants is inherited in a Mendelian fashion. If this is true it is not in- 

 conceivable that the height at various growth stages or. in fact, the 

 manner of growth is also dependent upon similar internal factors. 



The theory developed, especially by Emerson and East, to account 

 for the so-called 'blended' inheritance of quantitative characters may be 

 stated briefly as follows. It is assumed that the character, height of 

 plant for example, may be dependent upon several pairs of independent 

 factors and that these factors, each allelomorphic to its absence, are 

 cumulative in their effect upon the plant. It is also assumed that do- 

 minance is absent and consequently that the homozj'gous condition of 

 a factor will have twice the effect of the heterozygous condition. 



To illustrate this theory we may borrow the hAi^othetical case 

 given bj' Emerson and East. They assume that a plant genotypically 

 12 inches tall is crossed with a plant genotypically-28 inches tall. The 

 difference is 16 inches. If this difference is due to one pair of factors 

 then the large plant would have the constitution AA and the small 

 plant aa. Under the above theory the presence of each A will add 

 8 inches to the height of the plant. The heterozygous Aa would then 

 be 20 inches tall, providing of course there was no fluctuating varia- 



