Inheritance in the Higher Plants 93 



cerned in the hereditary transmission of a character. Com- 

 plexity shows only when the two parents differ in several 

 factors involving the same character. If they differ by 

 only one factor, inheritance may appear to be very simple; 

 but crosses between other individuals similar to the former 

 in appearance may show an entirely different state of affairs. 

 A very good illustration of what is meant by this statement 

 is the inheritance of the purple color of maize that occurs 

 in the single layer of cells immediately beneath the hull or 

 pericarp — the aleurone cells (Fig. 41). When an individual 

 of a variety containing the purple color is crossed with 

 certain white varieties, the hybrid is purple, showing dom- 

 inance of the purple character. The second hybrid genera- 

 tion produces three purple seeds to one white seed. Since 

 this is the normal monohybrid ratio, one would suppose 

 that the character in question is simple. This is only 

 apparently the case, however, for when the same purple 

 variety is crossed with other white varieties the ratio of 

 purple to white seeds is such that one knows the varieties 

 must have differed by two gametic factors affecting the 

 development of the purple character, instead of one. In 

 order that this matter may be made clear, the dihybrid 

 ratio must be explained. 



The dihybrid ratio is that obtained when the parents 

 differ by two character pairs. It is the algebraic product 

 of two (3 + 1) ratios. The chances are 1X1= /'^j that the 

 two dominant or presence characters occur together, 1x1 = 

 fV that the dominant character of the first pair meets the 

 recessive or absence character of the second pair, iX| = rV 

 that the recessive character of the first pair meets the 

 dominant character of the second pair, and jXj= i\- that 

 both the recessive characters occur together. If we let the 



