62 



The results actually obtained in the above case may be compared with 

 the theoretical expectation from a dihybrid crossing as follows: 



Results obtained. Theoretical expectation. 



Constant Red 25 = 7 9 



Segregating Red and White 13 = 3-7 3 



" 14 = 3-9 3 



Constant White 5 = 1-4 1 



When two wheat sorts having about the same average head density 

 were crossed, there were produced combinations having greater density than 

 either parent. Thus, when the sorts Bore and Extra Squarehead (See Fig. 29) , 

 having an average density of 32-8 and 34-6 respectively, were crossed, 

 combinations averaging in head density as high as 39-1 were produced. 

 Heads which were more open in character were also produced, so that the 

 progeny may be said to have exceeded the limits of density of the parents 

 in both directions (44 p. 282). 



When two sorts having about the same average length of straw were 

 crossed, there arose hereditary forms which were both longer and shorter 

 than either parents. 



Similar results were obtained when certain oat sorts having about the 

 same average length of hull or glume were crossed, forms which were longer 

 and others which were shorter than either of the parents being produced. 

 A good example is found in the crossing between Hvitling (0301) and Dup- 

 pauer (0926) (44 p. 286-7). The average length of the hull of these sorts 

 is 16.7 and 16.4 m.m. respectively. Among the progeny of the hybrids 

 there were isolated forms measuring, in the F 3 generation, as low as 14.4 

 m.m. and as high as 18.6 m.m., while the same differences were shown the 

 following year (F 4 ). Between these extremes there were also found numer- 

 ous hereditary gradations. An interesting fact revealed by these crossings 

 is that differences in the length of hull may be produced without effecting 

 in any way the length of the kernel. This is a good example of the inde- 

 pendent nature of different characters. 



When the two Svalof oat sorts Bell No. II and Great Mogul were crossed, 

 a number of combinations of the side-panicle type were produced although 

 both parent sorts belong to the spreading-panicle class. The assumption 

 here is that each parent possesses its own peculiar unit for spreading panicle 

 viz. A! and A 2 respectively. The presence of these two units together with 

 their corresponding absence, constitutes two character-pairs, which may be 

 represented in the following manner: 



Bell 11. Great Mogul, 



X 

 a 2 



