334 EXPERIMENT STATION RECOBD. 



Breadth of seeds was noted in the crosses of Missouri dent with California 

 pop and with Tom Thumb. In both cases Fi was distinctly intermediate be- 

 tween the parents in breadth of seed. Fj generations showed a markedly 

 greater variability than Fi or the parents. 



Four different crosses were employed in the studies of the inheritance of 

 height of plants. A peculiarity of these crosses was that in 3 of them the Fi 

 plants were almost as tall as the tall parent and in the fourth were considerably 

 taller than the mean of the 2 parents. It is stated that this increase in height 

 of the Fx plants over the mid-parental height was in no case ascribable to domi- 

 nance of tallness over shortness, but was due rather to increased vigor accom- 

 panying heterozygosis as indicated by the fact that in every case the mean 

 height of the F2 plants was about half way between the heights of the parents 

 and as also shown by the lack of skewness in F2 frequency distributions. Prac- 

 tically all of the Fs fraternities overlapped in height the inner extremes of their 

 parents. The F3 families were very diverse in height and in variability. 



A study of internode lengths explains the excess in height of Fi plants 

 over the average of the parent heights. Although the number of nodes in Fi 

 was apparently always distinctly intermediate between the parent numbers, the 

 internode length was so greatly increased by heterozygosis that Fi plants were 

 often nearly as tall as the tall parent plant, and always taller than the average 

 of the parent heights. 



In 2 crosses, one parent of which produced numerous tillers and the other 

 few tillers, Fi was intermediate in nnmber of stalks per plant. In both crosses 

 F2 was more variable than Fi and in one cross the Fj range was from 1 to 8 

 stalks, while 5 was the largest number observed in the parent variety that 

 tillered most freely. Among the Fs families a few were practically one-stalked 

 types and a few others had a somewha.t larger mean nmnber of stalks than the 

 tillering parent and a range of variation so great as to suggest the possibility 

 of isolating by selection a type with a still larger number of stalks. On ac- 

 count of the fact that In one cross the tall parent was a few-stalked type and 

 the short parent a many-stalked type, the 2 parent varieties did not differ 

 greatly in total length of stalks per plant. 



In earliness Fi plants were intermediate between their parents and the F. 

 generations more than filled in the gap between the parents in all cases where 

 exact records were made. It is observed that numerous apparent correlations, 

 genetic as well as physiological, have been encountered in these experiments 

 and many of them' have been noted incidentally in the detailed discussions of 

 results. 



" We have reason to believe, for instance, that length of ear is directly cor- 

 related with height of plant and inversely correlated with number of rows per 

 ear. Number of rows seems also to be related in some way to the character of 

 the endosperm, since in some crosses segregates with a large number of rows 

 have dent grains while those with few rows have flinty grains. It is apparent 

 also that, while height of plant and number of stalks per plant may not be 

 directly related, number of stalks and diameter of stalks are negatively cor- 

 related. Our records indicate that there is little if any correlation, either 

 genetic or physiological, between duration of growth and internode length. 

 There is also little or no physiological correlation between duration of growth 

 itnd number of nodes, but apparently a distinct genetic correlation between these 

 2 characters. In 1911, families of corn, which from previous selflng were ap- 

 proaching a condition of homozygosis of factors for size and duration of growth, 

 showed a slight negative correlation between number of nodes and duration of 

 growth, while F2 families, heterozygous for both number of nodes and for dura- 

 tion of growth, showed a marked positive correlation between these characters. 



