Blakeslee: Corn and Men 



515 



readily suppressed than the female 

 ears. Crowding is a compound influ- 

 ence. Inability to obtain sufficient 

 moisture or food constituents from the 

 soil, an accumulation of poisonous ex- 

 cretions from the roots, the lack of 

 sufficient light and air, may all be re- 

 sponsible in greater or less degree for 

 the observed effect. 



THE FORCE OF HEREDITY. 



But while environment is a potent 

 cause of variation, heredity is still 

 more important. The diversity of a 

 kitchen garden with its regular rows of 

 beets, corn, beans, and cabbage, is 

 primarily due to the different hereditary 

 characters bound up in the different 

 kinds of seed that were planted. A 

 cabbage seed will grow into a cabbage 

 and not into a com plant merely be- 

 cause its ancestors were cabbages and 

 not corn. Not only are the different 

 species of plants distinct on account of 

 heredity, but the different cultivated 

 varieties as well. In figure 15 is shown 

 a plant of the Tom Thumb variety of 

 pop corn beside a plant of the Learning 

 dent corn. 



The Tom Thumb variety was grown 

 in hills under the same favorable garden 

 conditions as the tall Leaming corn 

 already seen at the left in Figure 13. 

 The environment is practically the same 

 for the two forms, and the small size 

 of the pop corn is due to the fact that 

 the seed they were grown from was 

 produced by a small-sized variety. It is 

 perhaps fruitless to debate whether in 

 corn environment is the more important 

 or heredity. The latter has brought 

 about the difference in height between 

 the tall Leaming and the dwarf pop corn. 

 The former is responsible for the effects 

 of crowding shown in Figure 13. 



But heredity must not be considered 

 as effective only in the broader groups 

 known as species and varieties. Each 

 variety is doubtless a complex of many 

 mingled types which have not been 

 separated. Thus several races have 

 been isolated from the tall Leaming 

 com of Figure 13. Of two such races 

 picked out by the Illinois Experiment 

 Station, one forms high ears, the other 

 low ears. Likewise, from the same tall 



variety there have been separated out 

 races that differ in the storage products 

 in the kernels; one with a high, another 

 with a low, oil content ; one with a large 

 proportion of protein, another poor in 

 protein. The plants of these races 

 differ thus chemically because of hered- 

 itary differences in their parentage. 

 Heredity as a factor in the diversity in 

 living forms is always present. When 

 environment is the same, heredity is 

 the sole cause of variation. Usually 

 both are effective. 



Let us return to the students shown 

 in Figure 12 and see if we can discover 

 which factor, heredity or environment, 

 has been the more important in causing 

 their differences in height. One from 

 either extreme of the curve kindly con- 

 sented to investigate the heights of 

 his relatives with the results shown in 

 Figure 14. The short student was 19 

 years old and the tall student was 173^. 

 Squares indicate men and circles women, 

 the figures underlined are stocking feet 

 measurements. By estimating whether 

 an uncle or a grandfather was shorter 

 or taller than the father, a fair degree 

 of accuracy was obtained of members of 

 the family that could not be directly 

 measured. 



An inspection of the pedigrees shows 

 that the small student comes from a 

 short family. Except for a half uncle 

 who was of about average height (5 ft. 

 8 in.), all his relatives of whom records 

 could be obtained were undersized and 

 none was over 5 ft. 6 in., which is about 

 two inches below the average. 



The tall student whose pedigree is 

 given on the right has an entirely dif- 

 ferent ancestral history. Six footers 

 run in both sides of the family. His 

 great grandfather was reputed to be 

 6 ft. 4 in. in his stocking feet and the 

 tallest and strongest man in his town- 

 ship. His brother, at present only 13 

 years old, is 5 ft. 7 in. and would now 

 pass in his family as a relatively tall 

 man had he been bom into the other 

 pedigree. 



WHERE ENVIRONMENT ENTERS. 



The data given confirm the more ex- 

 tensive evidence from other sources 

 that heredity is the prime factor re- 



