238 



THE AM ERIC AX NATURALIST [Vol. LIII 



white-stemmed aurea type, it is evident that we are deal- 

 ing with a clear-cut instance of Mendelian behavior, in 

 which greenness of stem and leaf is contrasted with the 

 character of white stems and a yellowish, chlorotic ap- 

 pearance of the leaves. Since these characteristics are 

 readily distinguished in plants in the seedling stage, only 

 five or six weeks after germination, this cross is espe- 

 cially favorable for the demonstration of simple Men- 

 delian behavior in all its phases. The technique of 

 crossing is simple, and many thousands of seedlings may 

 be gro\vn in a comparatively small area in a short time. 



SUMMAEY 



In crosses between a distinctive white-stemmed aurea 

 type and green-stemmed type of N. rustica the following 

 Mendelian relations were found : 



In plants the white-stemmed aurea type is recessive 

 to the green-stemmed type. 



F2 plants segregate into green-stemmed and white- 

 stemmed aurea plants. Approximately 25 per cent, of 

 the plants are aurea recessive. Some of the green plants 

 are homozygous for greenness of stems, etc., and some 

 aio heterozygous, again segregating into green and 

 white-stemmed aurea types with the same ratios ob- 

 tained in the generation. The extracted aurea re- 

 cessives of the F^ generation are homozygous with re- 

 spect to the character of white stems, etc., peculiar to 

 this type. 



In back crosses between a heterozygous F^ plant and 

 the dominant green-stemmed type, the progeny consists 

 of 100 per cent, green-stemmed plants. 



In back crosses with the recessive aurea type, the 

 ])rogeny consists of green-stemmed and white-stemmed 

 (iiirca i)laiits in approximately the expected ratio of 

 1 to 1. 



