10 INTROGRESSR^ HYBRIDIZATION 



nection is typical of many of the instances of hybridization 

 that have been carefully studied in the field. 



Riley made population samples of Fulva, HGC, and vari- 

 ous hybrid colonies. Table 1 shows the kind of basic data 

 that he obtained from a colony of HGC, a colony of Fulva, 

 and the two hj^brid colonies H-1 and H-2. For each plant he 

 recorded whether it was essentially like HGC, like Fulva, or 

 intermediate in its tube color, petal shape, stamen exsertion, 

 style appendages, and shape of crest. He also measured the 

 sepal lengths, recorded the ground color of the sepal with the 

 aid of a standard color chart, and determined the percentage 

 of fertile pollen in each plant. Table 1 shows the kind of re- 

 sults he obtained for ten plants from each of the four col- 

 onies. HGC is essentially uniform in all these characters. 

 Fulva was similarly uniform, varying only in whether the 

 plants were red or pale red. Scored by the same method, 

 the two hybrid colonies presented a very different picture 

 and (a most important point) they showed significant dif- 

 ferences between themselves. Both of them varied from 

 plant to plant, but the variation in Colony H-1 was many 

 times as striking. H-1 varied in its extremes for each char- 

 acter and in its combinations of characters. It will be noted 

 that there are no two plants with exactly the same combina- 

 tion of characters. 



Colony H-2 was much more uniform. Some of its plants 

 were indistinguishable from HGC; others showed a few 

 slight differences on close scrutiny; a few were clearly inter- 

 mediate ; and, in such measurable characters as sepal length, 

 the population as a whole is slightly more like Fulva than 

 HGC normally is. 



Table 1 shows that variation in fertility parallels the 

 morphological variation. Fulva and HGC have pollen of 

 high fertility; there is more sterility in the hybrid colonies, 

 and much more in H-1 than in H-2. 



To smnmarize all these facts in a rough kind of way, Riley 

 used a method originated by Anderson (1936(i) which is 

 described and discussed in Chapter 6. He arbitrarily as- 



