198 LOCK : 



between parents of incontestable specific distinctness, or, 

 failing that, to find some blended character, which should 

 remain constant in all the offspring of a hybrid when these 

 amounted to a considerable number. It may be stated at 

 once that the proof of this kind of blended inheritance is not 

 as. yet forthccming. On the other hand, the great majority of 

 the visible characteristics of the hybrids studied were so elusive 

 and difficult of definition that indications of the actual 

 probable method of inheritance have so far been obtained 

 in the case of a very few characters only. That most of the 

 characters which show signs of definite Mendelian behaviour 

 are characters of colour, and that allUhe colour characters 

 observed seem to show some kind of segregation, I am 

 inclined to attribute, not so much to any peculiarity in the 

 nature of colour characters as such, as to the much greater 

 readiness with which such characters can be recognized and 

 defined than is the case with almost any other features. 



For the study of the behaviour of crosses between forms, 

 which must be recognized by every botanist as species in the 

 strictest sense, no better material seems likely to be found 

 than the genus Nicotiana. Few genera, too, have been more 

 completely explored by the older hybridizers from Kolreuter 

 onwards. Since the revival of uiterest in Mendel's work, 

 however, the subject, so far as I am aware, has not been 

 touched, and the importance of dealing with large numbers 

 of individuals in the second and later generations was not 

 realized by the early workers. The amount of work which is 

 still required is very great — far more than can be adequately 

 dealt with by one person — and one of the chief objects of the 

 writer in publishing these early attempts at a Mendelian 

 analysis was that others might be found to undertake a part 

 of the burden. An excellent account of the crosses carried 

 out prior to 1881 is to be found in W. 0. Focke's Pflanzen 

 Mischlinge. 



2. -THE SPECIES EMPLOYED IN CROSSING. 



The classification here adopted is that of Comes in his 

 Monographic du Genre Nicotiana (Naples, 1899). This agrees 

 in the main with that of Dunal in De Candolle's Pvodroraus, 



