NOTE ON THE ORIGIN OF A MUTATION IN 

 THE SWEET PEA 



By R. C. PUNNETT. F.U.S. 



(With One Tcxt-fi^nre.) 



Many instances of the sudden appeanince of new forms in plants 

 and animals have been recorded in recent years, and spt'culation has 

 been rife Jis to the moment at which they may be regarded jus havin^^ 

 originated. Perhaps the view most favoured is that the new form takes 

 its origin from some abnormal division during the f(»nnati()n of the 

 gametes. Nevertheless there are biologists who havi' placed on rcconl 

 their opinion that it may occur at some other stage in the life-history 

 of the form that exhibits the new character'. The princij^il ditticulty 

 in coming to any decision on this point is that in almost all cases on 

 record the new character has not been first observed in accurately pedi- 

 greed stock. After observation it has frequently been made the subject 

 of careful experiments in order to test its genetic nature, but this of 

 course does not help us with the problem of its origin. Even in Droso- 

 phila, with its century of mutants, there does not appear to hv a case 

 where the new^ form can be traced backwards through definite indi- 

 viduals for several generations. For this reason I have thought it worth 

 placing on record the following facts in connection with the apjx'ai-ance 

 of a new form of sweet pea in pedigree cultures. The form in question 

 is the so-called " cretin," already described by Mr Bateson and myself 

 in an earlier number of this Journal'-. It is a monstrous form of which 

 the chief characteristic is the straight stigma protruding through tiie 



' See more especially Johannsen, /r« C'oH/e;rnf« InteruatiouaU de Geni^tique, Paris, 

 1911, aud Emerson, The American Saturalixt, June 1913. A Kood general discussion on 

 the subject is to be found in Baur's EittJUhruug in die erperimentelle Ver>rhungnUhre, 

 2 Auf. 1914, pp. 288 seq. 



- Journnl cj GenetirK, Vol. i. 1911. 



