Inheritance in the Higher Plants 105 



hybrid generation one ear like each original parent is 

 obtained out of every sixteen instead of every four (Figs. 

 46, 47). This inheritance is therefore dihybrid in charac- 

 ter. In like manner, a higher number of transmissible fac- 

 tors may affect the development of what is to the eye a 

 single character. 



Since dominance is not an essential feature of Mendeli- 

 anism, size characters may show intermediates or blends 

 in the first hybrid generation and still fulfil the essential 

 conditions of Mendel's law by recombining in such a fashion 

 as to produce individuals like either parent in the second 

 hybrid generation provided a sufficiently large number of 

 individuals to allow for the recombination of several factors 

 is grown in that generation. Such recombinations do occur 

 and can be shown by experiment. For example, the small 

 variety of corn, Tom Thumb, when crossed with a larger 

 variety like the Black Mexican (Fig. 48), gives a first hybrid 

 generation that is intermediate between the two parents. 

 One may call this a blended condition; yet if there were 

 blended inheritance this condition would be transmitted, 

 while if Mendelian recombination occurred, sizes compa- 

 rable to either parent would be obtained in the second hybrid 

 generation. Such extremes were obtained as is shown in 

 the figure. 



If the possible Mendelian interpretation of quantitative 

 characters has been made clear, the statement that Men- 

 del's law is probably universally applicable where sexual 

 reproduction occurs will not seem rash. There are still 

 some apparent exceptions to the law, but they are so few 

 that one may well believe we simply do not know how to 

 bring them into line and not that they are actual exceptions. 

 Of course it is quite likely that there are other laws which 



