IBS 



THE AMERICAN NATURALIST [Vol. XLV 



Table II shows a similar distribution of heights in 

 cross between no. 60, a dwarf pop maize commonly knowrn 

 as Tom Thnmb, and no. 54, a sugar corn known as Black 

 Mexican. The distribution of heights of no. 54 was ob- 

 tained in the same season as the F 2 generation. They 

 were both grown upon the same plot of ground in which 

 the soil appeared to be quite uniform. Unfortunately, 

 the exact distribution of the heights of no. 60 and of the 

 Fj plants which were grown in previous seasons, is un- 

 known. The range of the variates shown by the black 

 lines, however, is correct. Furthermore, from notes re- 

 corded at the time we know that the ¥ 1 generation was 

 comparatively uniform, the greater number of variates 

 being distributed around classes 67, 70 and 73 inches. In 

 this case, also, the effect of crossing is shown by the rela- 

 tively high plants of this generation. The plants of the 

 F 2 generation show a wide range of variation. The 

 highest individuals are practically the height of the 

 highest individuals of the taller parent, no. 54. The 

 lowest plants of F 2 do not reach the lower range of no. 60. 

 I interpret this as due to continued heterozygosis in other 

 characters and to physiological correlation. By the latter 

 term I mean that since the plants of no. 60 are very small, 

 F 2 segregates of the same size could only be expected 

 where the ears and seeds also are very small. But since 

 the ears and seeds of these plants also show segrega- 

 tion in new combinations, normal growth correlation 

 probably resulted in a somewhat larger average size. 

 For example, little 40-inch plants were found with ears 

 three times the length of normal ears of no. 60. It is 

 likely that such plants might have been smaller if they 

 had been recombined with the characters necessary for 

 the production of smaller ears. 



Table III and Figs. 1-4, show the lengths of ears in the 

 cross just described. In making this table the best ear 

 from each plant that bore a well-filled ear was taken. 

 The small ears, therefore, do not represent poor, unfilled 

 or supernumerary ears. The coefficients of variability 



