R. N. Salaman 35 



In 1908 two of the F' plants, viz. K^ and K'> both selfed and large 

 families were planted ; those of Z« did well, the K^ family fared badly 

 in the wet summer of 1909. 



K^ Family. K\ Plate XXIX, is a black (i.e. deep purple) potato. 

 Several seedballs were collected from the plants, and one coming 

 from a plant K^'-^^ was planted in its eutii-ety. Originally 301, there 

 wei'e harvested but 160 seedlings. The tubers of the F- family 

 separate at once into blacks, reds and whites in the proportion of 77 

 black, 29 red, 54 white ; the reds are either quite pale and similar to 

 " Flourball " or " Reading Russet," or they have more purple colour 

 and resemble " Red Fir Apple." 



Of the whites about one-sixth (9 in 54) are quite pure, i.e. no tinge 

 of colour can be seen in the tubers or eye before sprouting, whilst the 

 remainder may have a trace of colouring usually purple, in the eye or 

 the skin and more especially in any scars following a wound by fungous 

 disease or other lesion. Such pigment is minute in quantity and often 

 needs a lens to demonstrate its presence. The reds are roughly of two 

 kinds, a deep strong group, and a pale. The proportion between these is 

 23 deep red, and 6 pale red, and they can be classed fairly readily into 

 these main groups. The blacks are all alike, viz. deep purple. In con- 

 sidering the factors which underlie the phenomena of colour in the red- 

 and white-tubered potatoes we assumed the presence of the two factors 

 R and D. The purple potato is obviously bringing a fresh factor besides 

 these into the field and this new or " purpling " factor can be called P. 



If K^ has the gametic formula Pp, Rr, Dd, then on selfing we 

 should get plants or biotypes with the following gametic constitutions : 



27 plants of the composition PRD = purple. 



y » » 



" )> >> 



" I) )) 



" )) » 



3 ,1 „ 



3 „ ,1 



The numbers for the K"^ family are : — 



