MEXDKLL 1 A' BE HA 1 -lOE 



235 



DoMixAxcE OF Geeex Pla^tt Colok IX Plants of 

 Crosses 



In 1914 the writer made reciprocal crosses of this 

 white-stemmed, chlorotic aurea type of N. rustica, with 

 green-stemmed, green-leaved type, and several hundred 

 plants were grow^n in the field at Arlington, Va., dur- 

 ing the season of 1915, All the F^ plants were green in 

 color, whichever type was used as the seed-bearing par- 

 ent. It was at once evident that the white-stemmed, 

 chlorotic, aurea character behaved as a simple recessive 

 to normal greenness of stem and leaf. To determine 

 more fully the Mendelian behavior of this cross an anal- 

 ysis of the F^ and F^ generations was made. 



Segregatiox IX Y- Plaxts 



In the F- generation, green- and white-stemmed aurea 

 plants appeared. So distinct i^; the white-stemmed re- 

 cessive that four or five weeks nftor ori-mination, the 

 young plants can be readily disthignished from the 

 green-stemmed types. This made the growing and han- 

 dling of large numbers of plants a comparatively easy 

 matter, since it was only necessary to grow them to the 

 size of small seedlings and obtain counts when they were 

 four or live wec^ks old. In the folhnving table an analysis 

 of L»:),(»no F> plniits is slunvii. 



From this (hita it is cx idciit tliat the recessive white- 

 stemmed (i)in-<i tyi)e of nisficti appeared in numbers ap- 

 proximating very closely the theoretical Mendelian ratio 

 of 27) ])vv ('('111., since in a population of 25,000 plants, 

 24.;)1 per cent, were of the white-stemmed, aurea type. 



