26 Genetic Studies in Potatoes 



vertically. It is as if the plant wanted to stand up but couldn't, and 

 after falling to the ground was making a fresh effort to regain the 

 normal position, whereas in the other variety it has neither power nor 

 desire to lead the " upright " life. The " prostrate " indeed not only falls 

 to the ground but adapts its development in harmony with the new 

 conditions. 



For the second variety we suggest the term "procumbent" in contrast 

 to the " prostrate " variety previously described. 



Here then are two varieties sharing one character in common, 

 deficiency of skeletal structure, but differing as we would suggest in 

 their tropic reaction. Just as the stolon, the underground stem of the 

 potato, has changed its tropic reaction, so has the aerial stem of the 

 true " prostrate." Whilst the " prostrate " variety was only observed once 

 in the history of our cultures and from that time specially bred, the 

 " procumbent " has been noticed several times. 



Genetic Relations. 



The original family of " prostrate " plants came from the self-fertiliza- 

 tion of a plant raised at Barley, Hertfordshire, in 1909^ This parent 

 we shall refer to as M5 535, following the original nomenclature. Its 

 origin may in turn be traced back to three cultivated varieties — Flour- 

 ball, Queen of the Valley and Bohemian Pearl. One would naturally 

 expect to find the parent M5 BS5 of this selfed family exhibiting the 

 " prostrate " character. Unfortunately we have no evidence on this point, 

 as stock of this plant was lost before attention had been drawn to the 

 character in question. Among its ancestors again there is no record of 

 the " prostrate " habit. Although it is possible that the character was 

 missed it is on the whole improbable as M5 was certainly " upright," 

 and we have never met with the " prostrate " character in any Bohemian 

 Pearl (B) seedlings. 



The results of breeding tests with " prostrate " plants will now be 

 described. Most of the seed was obtained from unprotected flowers, 

 although numerous attempts were made to obtain seed from flowers 

 protected with parchment bags. As there is a risk of accidental pollina- 

 tion by insects — small it is true but certainly not negligible — we took 

 the precaution of saving the seed of individual berries separately, for in 

 this way we could more closely compare the results of similar pollinations. 

 Of the thirty-one " prostrate " plants obtained from the selfing of M5 BS5 

 and transplanted into the field in 1911 only two flowered. The season 

 ' Salaman, R. N., Journal of Genetics, 1910, Vol. i. No. 1.. 



