218 



The J(jurnal of Heredity 



'I'lic results sliow n in TahK' l\ coin 

 cidf fully with those exhibited l)\ 

 Table 111. It should be remarked thai 

 in all of the above tables the i^rou]) 

 headed "mixture of hard, intermediate, 

 and soft." contains at least three types 

 of i)lants. as follows: (1) Those bear- 

 ing a mixture of hard and intermediate 

 t^rains; (2) those with a mixture of 

 hard, intermediate and soft <jrains. and 

 ( ,^ ) those with a mixture of interme- 

 diate and soft grains. These types so 

 insensibly grade into one another that 

 it was ft)und impracticable to sei)arate 

 them. It may. however, be stated that 

 where the offspring of a given mother 

 plant segregate only into ])lants with 

 all hard seed, and those with a mixture 

 of types and none with all soft seed, the 

 seeds on those plants with mixed ty{)es 

 tend toward the harder limits of the 

 series. /'. c. they fall into typt' ( 1 ) of 

 the series described above. W hen the 

 olTspring of a single mother i)lant seg- 

 regate into plants having all hard seeds, 

 plants with a mixture of types and 

 plants having all soft seeds, then many 

 of the i)lants having seeds of mixed 

 types show every gradati(jn of seed 

 type from hard through intermediate 

 to soft. Again, when the offspring of 

 a single mother plant segregate into 

 l^lants having a mixture of seed types 

 and plants with all soft seeds, the seeds 

 on the ])lants having a mixture of types 

 tend stronglv to fall into the softer 

 end of the series, ;. (•.. to consist ol <'i 

 mixture of intermediate and soft seeds. 

 The character of the seed on mother 

 plants having a mixture of seed types 

 gives a strong indication of the kind 

 of segregation to be expecti-d in the 

 offspring. If thev fall within tin- 

 harder en<l of the si-ries thev tcn<l to 

 give only ])lants with all hard seeds. 

 and plants with a mixture of hard and 

 intermediate seeds. If tluv lie nearer 

 the softer end of the series, then the 

 offspring tend to segregate only into 

 plaiUs having a mixture of intermediate 

 and soft seed and plants with all soft 

 fu-eds. I'"inally, if tin- mother ])lant 

 contains all types of si-ed, then all tvpt'S 



of plants nKi\- bi- expected among the 

 otTspring. The continuous intergrada- 

 tion of seed types would render any 

 riumerical sei)aration i)urely arbitrary. 

 .\ judgment of the genetic comi)osition 

 of the parent by the behavior of its 

 offspring is. therefore, here, as in many 

 other cases, llu' onl\' sure means oi 

 analysis. 



I'wo iwcToi^s .\i'i'i;.\k i'Ki:si:xr 



.\ genetic analysis (jf the data pre- 

 sented can be made by assuming that 

 the relative proportion of gluten and 

 starch in the endosperm of the wheat 

 varieties studied is controlled by two 

 factors, tile intensity of the action of 

 which may be varied within somewhat 

 narrow limits by environic conditions 

 in the same manner that the intensity 

 of action of other factors governing 

 r|uantitative characters are varied by 

 their environment. Ihe combination 

 of these variations. i)artly genetic and 

 partly environic. are. therefore, amply 

 sufficient to accotint for tlie intergrada- 

 tion of grain types and the impossibility 

 (jf making exact numerical se])arati<)ns. 



With these ideas in view, let us now 

 assume two factors for increasing the 

 j)ercentage of tarch .A and 15 having 

 incom])lete dominance over their ab- 

 sence and being accumulati\e in their 

 action. Let us su])pose further that 

 ( 1)\- the standards of comi)arison used 

 b\- the writi'r ) the presence of three 

 -A's together with at least one \\ in 

 the endosi)erm ct-lls (assuming double 

 fertilization) of a grain were suf^cient 

 to cause it to be classed ;is so It. whereas 

 less than three .\'s and I'.'s comUed 

 together would result in an endosperm 

 which would be- graded as "hard." .Ml 

 other seeds would !)e giaded as "iiUer- 

 mediate." 



The genetic composition of the 1*"., 

 embryos, and. hence, of the somatic 

 tissue of the V.^ i)lants arising there- 

 from, together with the genetic sti'UC- 

 lure of tin- I'udosptMin of the seeds 

 and embrvos borni- on these plaiUs. can 

 be placed in tabular form as follows: 



