180 University of California Publications in Botany [Vol. 5 



undoubtedly partially sterile. This supposition is supported by 

 the fact that generally only a few axillary buds are found 

 to be produced at the bases of maturing seed capsules in 

 the iV. sylvestris parent and that where a Hower does develop 

 from such a bud reduction in its size, noted under similar con- 

 ditions in the N. Tahacum parental varieties, is not so striking. 

 The factor introduced by the ^V. sylvestris parent thus may stand 

 for the recessive condition of this abnormal-flower character. The 

 normal production of seed may, also, be looked upon as a separ- 

 ately inherited tendency which in these sterile hybrids appears 

 to be in a latent condition or possibly represents the recessive 

 member of another Mendelian pair with reference to these 

 hybrids. Though it may not be profitable to push the analogy 

 too far it is to be noted in this connection, that N. sylvestris has 

 the very interesting tendency, strongly emphasized in our cul- 

 tures, of reproducing ' ' vegetatively " from the roots year after 

 year and that the hybrids made with N. sylvestris as one or other 

 parent also possess quite markedly this peculiarity which is 

 rather unusual in the genus Nicotiana but is common in other 

 genera of the Solanaceae. Thus, following out the analogy, it 

 may be possible that sexual reproduction vs. its absence (vegeta- 

 tive reproduction) constitute the members of a Mendelian pair 

 and that the absence of vigorous seed production in these hybrids 

 represents a recessive condition. While the experimental basis 

 for these suppositions is rather vague the facts brought out in 

 connection with them may prove to be of some importance with 

 reference to the well recognized sterility of hybrids in which A\ 

 sylvestris is involved as a parent. In this connection it may be 

 said that a considerable variety of experiments are at present 

 being carried on in the effort to bring about normal seed produc- 

 tion in the case of these "sterile" hybrids and also that a 

 quantity of cytological material has been collected from them and 

 from the parental varieties in the hope that a considerable mass 

 of data on the nature of sterility in such hybrids may be at hand 

 before the end of the coming year. The above, in general, is 

 interesting principally in that it adds weight by analogy to the 

 point of view which looks upon the "unit-character" not as an 

 "atom" but as a "molecule" or indeed as a heritable potentiality 



