2io MENDELISM 



(long pollen), in the other it is approximately spherical 

 (round pollen). Sweet-peas normally undergo self- 

 pollination, so that the two types naturally remain 

 distinct. Let us see what happened when the long- 

 and the round-pollened forms were crossed together. 



The cross-bred plants (FJ had coloured flowers 

 flowers of the old - fashioned purple type known to 

 florists as Purple Invincible, which is characterized by 

 a purpk standard and blue wings. The pollen pro- 

 duced by these plants was of the long type. Thus as 

 regards the shape of the pollen grains there was simple 

 dominance. But the union of two white-flowered 

 types has given rise to a series of plants all possessing 

 a definite colour character purple with blue wings. 

 This character is very probably the same as that 

 exhibited by the common ancestor of all our cultivated 

 sweet-peas. Here, then, we seem to have a clear case 

 of reversion to the ancestral type on crossing. We 

 shall find that the Mendelian principles will enable us 

 to arrive at a clear conception of the mechanism of 

 this process. 



The cross-bred plants were self-pollinated, and in F, 

 the following types made their appearance in approxi- 

 mately the proportions given : 



Purple Invincible ... 8n /3\ 



f or 1 

 Picotee 27) (i } 



Painted Lady ... 27 

 Tinged white ... 9 



White... 112 



