UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



BOTANY 



Vol. 5, No. II, pp. 301-346, plates 37-48 January 17, 1917 



THE NATURE OF THE F: SPECIES HYBRIDS 



BETWEEN NICOTIANA SYLVESTRIS AND 



VARIETIES OF NICOTIANA TABACUM 



WITH SPECIAL REFERENCE TO THE CONCEPTION OF 

 REACTION SYSTEM CONTRASTS IN HEREDITY 



BY 



T. H. GOODSPEED and R. E. CLAUSEN 



The partially sterile F^ hybrids between Nicotiana sylvestris and 

 various varieties of N. Tahacum have been a subject of investigation 

 for a number of years in the University of California Botanical Gar- 

 den. As stated in a previous paper (cf. Goodsi)eed and Ayres, 1916), 

 the problems which have arisen in connection with a study of these 

 hybrids are being attacked from a number of points of view. The 

 present report is the first which takes up definitely the data bearing 

 on the genetic aspect of the general problem and, in this particular 

 connection, it cannot claim to be more than introductory in nature, 

 while it is equally concerned with providing evidence in support of 

 a theoretical contention recently advanced (cf. Goodspeed and 

 Clausen, 1916). In this latter discussion it was pointed out that 

 hereditary behavior in certain cases may, for a thoroughly consistent 

 explanation, be looked upon as a result of the interaction of distinct 

 reaction systems rather than as a result of the expression of specific 

 factor differences within a common Mendelian system. These two 

 rather fundanuintally different conceptions may be tlioiiglit of as 

 applicable to species hybrids and other wide crosses in the first in- 

 stance and to tlie results of varietal crosses in the second. Thus, one 



