SPECIES CROSSES IN THE GENUS NICOTIAN A. 201 



Numerous hybrids were also obtained between varieties of 

 N. rustica, N. langsdorfii, and N. tabacum. All such varietal 

 crosses (with one peculiar exception noted below) appeared to 

 be quite fertile with their own pollen. 



From the point of view of the student of heredity, com- 

 pletely sterile hybrids are of interest chiefly as combinations 

 to be avoided. On the other hand, hybrids which exhibit 

 partial sterility are worthy of specially careful examination, 

 as being likely to throw light on one of the most important of 

 specific problems. This can only be done, however, where 

 there are facilities available for carefully nursing the seedlings. 

 Under the conditions at present obtainmg at Peradeniya, I am 

 able to do little, except with the more fertile forms. I would 

 therefore specially recommend such a cross as N. rustica X 

 paniculata to students of heredity. In spite of the excellence 

 of Kolreuter's work upon this conibination , carried out nearly 

 150 years ago, there is a great deal still to be learnt from an 

 examination of its progeny in the light of modern knowledge. 



The first point which strikes an observer familiar with the 

 offspring of crosses between domestic varieties is the inter- 

 mediate character shown by all the above hybrids. Speaking 

 in general terms of the adult plants, it may be said that 

 practically every character of every hybrid approaches the 

 mean between the corresponding characters of the parents.* 

 The fact that I was at one time doubtful whether my seedlings 

 of N. rustico-paniculata had not arisen by accidental self- 

 pollination of N. rustica (in spite of great care in the mani- 

 pulation) points to a predominating influence of the mother 

 upon the seedling characters of this particular cross. In the 

 adult state, however, it was impossible to discover a single 

 point in which ^these hybrids were not intermediate between 

 their'^parents. 



In describing the degree of intermediateness of a hybrid 

 plant a great deal clearly depends upon the individual judg- 

 ment of the observer. The following quotation in illustration 

 of this point is from Gsertner's Bastarderzeugung, p. 252 : — • 



■'ifAn. example of the variety of diverse opinions is afforded by 

 Nicotiana rustico-paniculata, regarded by Kolreuter as occupying 



* There are a few exceptions to be noted later on. 



