Mendel's law of heeedity and horticulture. 43 



BL 

 DL 



Erect Cupid, cream. 



T 



P 



W 



C 



R 



B 



D 



L 



Bush, cream. 



Oupid, cream (e.g. Prlnirose Cupid). 

 Erect Oupid, pure white. 

 Erect Oupid, cream. 



All absent 



Erect Oupid, cream. 



It will be observed that the various relations and interactions 

 between the factors in the case of the sweet pea are quite different from 

 those in the snapdragon. 



Tlius T with P gives the ordinary " Tall " habit, T alone gives 

 " Busli " -habit, P alone gives the ordinary " Oupid " habit, while 

 absence of both T and P gives the form Erect Oupid." Presence of 

 W gives a pure white ground in the flowers, while absence of W gives 

 a cream ground. 



0 with R gives red colour in the flower, while in the absence of 

 either 0 or R the flowers are pure white or cream, according to the 

 presence or absence respectively of W. 



B is only manifested in the presence of both 0 and E giving purple 

 colour. 



D is only manifested in the presence of both 0 and E giving 

 intensified colour. 



L is only manifested in the presence of 0, E, and D together, giving 

 light-coloured wings. 



As in the case of the snapdragon, only a single presence of the 

 eight factors is given in the above table for the sake of simplicity. In 

 accordance with Mendel's law it will, of course, be understood that 

 a pure-bred form would have a double presence of each factor, thus the 

 pure-breeding wild form would be constituted TTPPWWOOEEBB 

 DDLL and so on with the others. So far, however, the single 

 presence of these eight factors apparently gives the same visible result 

 as the double presence, but the breeding results would, of course, be 

 quite different. All the above combinations of factors may occur with 

 either a double or a single presence of each factor in various combina- 

 tions in accordance with Mendel's law. 



The results of these experiments with the snapdragon and the 

 sweet pea show that the numerous and varied garden forms that 

 have arisen from time to time under cultivation are simply due to 

 the dropping out of certain unit factors. It would appear, there- 

 fore, that the evolution of the snapdragon and the sweet pea under 

 cultivation, so far from being an increase of complexity, as one might 



