1913] Goodspeed: Nicoiiana Hybrids 177 



be maintained for a time only, simply by reason of the distinction 

 in the method of accumulating the experimental results, between 

 the experiments where quantitative and in those where quali- 

 tative characters are being dealt with. Experimental results seem 

 to have established a distinction between characters which appear 

 to be tangible realities in pure bred parental strains, "atomic," 

 and which can be spoken of as "unit-characters" — i.e., "units dis- 

 tinct and indestructible which may meet in fertilization but 

 separate again at the formation of gametes" (Castle, 191], p. 

 38), and characters which appear to be just as tangible realities 

 in the parents but are really "molecular" in structure, capable 

 of infinite divisibility and, as characters, really exist in the 

 parents themselves in possibility but not in reality — i.e., as 

 potential characters. 



"With reference to the divisibility of what might be called a 

 ' ' physiological unit-character ' ' an interesting bit of experimental 

 evidence has recently appeared among the Nicotiana cultures in 

 the Botanical Garden of the University of California. In 1910 

 and 1911 a number of cross pollinations, back and forth, be- 

 tween N. sijlvestris and a number of N. Tahacum-varieties were 

 made by Professor Setchell. Ten groups of hybrids, the results 

 of these crosses, are growing this year (1912). Among them are 

 those which involve N. Tahacum var. macrophylla (U.C.B.G. 

 22/07), (Setchell, 1912, p. 8), .V. Tahacum var. cahjcina (U.C. 

 E.G. 110/05) (loc. cit., p. 6), A^ Tahacum "Maryland" (U.C. 

 E.G. 78/05) (loc. cit., p. 5), etc., with N. sylvestris (U.C.B.G. 

 107/01) (loc. cit., p. 29), as either the male or female parent. 

 These hybrids, in each case, are practically sterile, at least as com- 

 pared with the heavy seeding character of the parents. The 

 flowers, in most cases, fall a short time after anthesis, the pollen is 

 more or less scanty and in general they are of the type of hybrids 

 of various species of Nicotiana with N. sylvestris which have pre- 

 viously been reported to be completely sterile (cf. Baur, 1911, p. 

 224, East and Hayes, 1912, and the literature there cited). 



It has been noticed in all the N. Tahacum-Yarietiefi and, to 

 a lesser extent, in A^ sylvestris that as an infloresence, consisting 

 often of from 40 to 50 flowers, passes from the flowering to the 

 seeding stage a few flowers will often appear from flower buds 



