388 



HYBRIDS, SEGREGATION 



intermediate type, whilst the remainder consist of Star and 

 Chinese Primroses in equal numbers. 



Hybridisation experiments not only teach us the principle of 

 segregation of characters, but also emphasise the fact that 

 external appearance is no certain guide to the internal charac- 

 teristics. This is perhaps most strikingly illustrated by the 

 effect of crossing certain pure-bred strains of white-flowered 

 Sweet Peas. We should naturally expect all the offspring to 



F2.. 



Fig. 22C. — Hybrids between Chinese [Primula sinensis) and Star Primroses 

 (P. stellata). At the top the two parents, the Chinese (C) with large, 

 rather wavy, much crenated petals, and the Star (5.) with smaller flat 

 petals exhibiting only a notch. The Fi generation is intermediate 

 between the two in these respects. In the F2 segregation takes place 

 in the usual way. (After Punnett.) 



be white-flowered too, but in reality all have coloured flowers, 

 with a purple standard and blue wings. Here, clearly, the parents 

 possess characters which in combination lead to the production 

 of a coloured flower, though when separated they produce no 

 visible effect. By breeding plants the limited knowledge of the 

 constitution of any organism, which is obtained by mere exami- 

 nation of external or internal structure, can thus be to some 

 extent supplemented. 



When two varieties cross in nature, the appearance of the 

 hybrid is of course influenced by all the characters present in 



