1436 



PLANT BREEDIXCr 



bled the mother plant 07 in appearance and size and others exhibited more 

 or less variation in shape and colour. 



2) 17 healthy plants with violet tubers. 



3) I plant possessing normal tubers, with the exception of three of 

 a whitish 3^ellow colour. The latter were planted, and in 1914 produced 

 pure descendants with whitish-yellow, healthy tubers. 



4) I almost healthy plant, showing evident marks of variation : 

 violet petioles ; glabrous and shining leaf blades, very elongated ; growth 

 rapid and exuberant ; tubers of varioiis shapes — normal violet and roun- 

 ded, deep violet and rather oval, red and vevy elongated. These were 

 all planted separately in pots, and in 1914 the crop showed that 



a) the red colour is tramsitted by the red tubers to their descen- 

 dants, which are more or less liable to " mosaic disease ". 



b) the violet tubers produce plants bearing violet tubers, but these 

 plants are clearly divisible into two groups — healthy and susceptible. 



From these data the following genealogical tree may be built up : 



mother plant 07, susceptible 

 1911 



1912 



i 

 76 



susceptible 

 violet tubers 



I susceptible 

 (32 violet tubers) 

 (3 whitish j'ellow) 

 (tubers) 



I ! 



I healthy 17 



21 red tubers healthy 



27 violet violet tubers 

 tubers 



1914 



1914 



This biological study is being continued with a view to establishing the 

 character and number of the "determinant" elements in the appearance 

 of new characters. 



This case of variation is of some scientific importance and is also of 

 much practical value, as it demonstrates the possibility of isolating and 

 fixing a variety' of potato which is healthy and not susceptible to mosaic 

 disease. 



