THE AMEBIC AN NATURALIST 



[Vol. LI 



a large number of elements whicli bear a more or less spe- 

 cific relation to one another. This is the important physi- 

 ological conception which has grown out of the vast 

 amount of work which has been done in recent years in 

 the analysis of the hereditary material. This is no new 

 contention ; it has been advanced and ably advocated by 

 many investigators, but we feel that certain consequences 

 of this conception have not been given the consideration 

 their importance deserves. For if this conception be 

 valid then it should not be possible, in certain cases at 

 least, to shift and recombine the elements from which 

 systems have been built up in the haphazard way that 

 some advocates of Mendelism have attempted to do. If, 

 for example, it is possible to obtain hybrids involving not 

 a contrast between factors within a single system, but a 

 contrast of systems all along the line, then it is obvious 

 that we must consider the phenomenon on a higher plane, 

 we must lift our point of consideration as it were from the 

 units of the system to the systems as units in themselves. 



Our attention has been called to this extension of the 

 Mendelian conception by the behavior of species hybrids 

 of Nicotiana which have been studied at the University 

 of California during the past six years. This study has 

 been concerned particularly with hybrids between N. syl- 

 vestris and varieties of N. Tahacum. These species, the 

 former represented in the collections of the University of 

 California Botanical Garden by a single type and the 

 latter by a considerable variety of distinct forms, belong 

 to entirely distinct sections of the genus Nicotiana and 

 differ in important particulars which have been described 

 elsewhere (Setchell, 1912). Ooodspeed (1913) has studied 

 a large number of different reciprocal hybrids between 

 sylvestris and various of the distinct varieties of Taha- 

 cum. These hybrids are all partially sterile. It is pos- 

 sible to obtain a few viable seeds from open pollinated 

 flowers and from those pollinated with Tahacum and syl- 

 vestris, but it has never been found possible to obtain any 

 selfed seed. The phenomena displayed by these hybrids 

 in development and inheritance admit of a consistent ex- 



