A LECTURE ON THE HEREDITARY CHARACTERS IN THE POTATO. 39 



On four different occasions coloured families have been made by 

 uniting white-tubered plants, a phenomenon entirely in accord with the 

 experiments of Bate son and others in sweet peas and Primulas. In 

 addition to these factors there are probably diluting factors which react 

 on the purple, but these have not been fully investigated. 



It was found that *S'. etuherosuin of Lindsay is in possession of a 

 factor rendering white dominant to purple, and I think it probable that 

 this inhibitor of purple is an element not normally contained in any of 

 the domestic varieties. 



Coloured Flesh. — Eed and purple coated tubers are often similarly 

 pigmented in their flesh, but this pigmentation can be clearly shown 

 to be due to a single pair of factors, and it is thus possible to produce 

 a dark-coated tuber which is absolutely unpigmented inside, on the one 

 hand, and, on the other, a white potato, colourless inside, which, when 

 mated with any coloured variety, will cause all its coloured-coated 

 offspring to have coloured flesh. 



Resistance to the Attacks of Phytoplithora hifestans. — My remarks 

 on this subject must be brief, and made with all possible reserve 

 and caution. In 1909 and 1910, when the disease was exceptionally 

 severe, I found that one-fourth of the seedlings of S. etuherosum were 

 unaffected by disease, whilst the remainder perished. From these 

 apparently immune individuals numerous crosses have been made and 

 large families formed. As there was no disease in 1911, their resist- 

 ance could not be tested. In this season these first-generation plants 

 are being regrowm, and, in addition, several second-generation families, 

 in which it is hoped the recessive quality of immunity may segregate 

 out. So far I have dealt only with the analysis of characters. My 

 work this year and in the future will be directed rather to the synthesis 

 of characters, the grouping together in one plant of all the wished- 

 for qualities that are controlled by genetic factors in a pure state. The 

 final result of such a synthesis should be to produce a potato which 

 will not only be good in all respects, but which will repro'duce itself 

 just as truly from flower seed as from tuber culture. 



One cannot, however, at this juncture say more than that it is 

 conceivable that a really immune potato, to which .all other desirable 

 qualities may readily be added, is not an improbable feature of the 

 future. Should such a result ever be attained, we should be immeasur- 

 ably indebted to the silent work of the patient and noble priest of 

 Briin. 



