Varietäten, Descendenz, Hybriden. 223 



tation, Blaringhem züchtete diese und es liegen bereits 3 Gene- 

 rationen mit 220 Individuen vor. C. Heegeri Solms-Laub. erwies sich 

 aber auch als konstant. Diese Beispiele zeigen, dass Capsella auf 

 die Frage, wie neue Arten entstehen, antwortet: durch Mutation. 



Matouschek (Wien). 



Goodspeed, T. H., Quantitative s tu dies of inheritance in 

 Nicotiana hybrids III. (Univ. Calif. Publ. Botany. V. 6. p. 223- 

 231. 1915.) 



The author has made over 13000 measureraents of spread and 

 lenght of coroUas of flowers borne upon three flower-size varieties 

 of Nicotmiia acuminata and on the hybrids made between them. The 

 parents, one F^ and one F2 population and the F3 were grown in 

 the Summer of 1913. The tables of Variation given in this and fore- 

 going papers, seem to indicate the foUowing facts: 



The Fj-generation of the N'. acuminata flower-size hybrids shows 

 a ränge of Variation as greai as and offen greater than the parent 

 plants in corresponding years. The mean flower-size may be approxi- 

 mately the mean of the parent flower sizes or it may not. 



The Fg-populations in some cases show a remarkable increase 

 in the ränge of variability as compared with the parents and F^- 

 hybrids. This ränge in no case is equal to the total combined ränge 

 over which the variability of both parents extends. Thus in some 

 cases the means of individual Fg-plants may be as small as or 

 smaller than the mean of the smallest-flowered parent plant, but 

 in no case, for the same F2-distribution, is the mean flower-size of 

 the largest-flowered Fg-plant as great as the mean of the largest- 

 flowered parent individual. Indeed in only one case do Fg-indivi- 

 duals approach the size of the largest-flowered parent plants and 

 at the same time show individuals with means within the small- 

 flowered parental ränge. A certain proportion of this increase in 

 variability in Fg-populations may be ascribed to the active interfe- 

 rence of various external and internal factors attending develop- 

 ment. It is significant in this connection that the flower-size of the 

 Fg-hybrids shows in the greater number of cases an increase of 

 variability toward the smaller end of the parental ränge. 



Though a number of Fg-families were grown, it was not found 

 possible to measure flowers on more than one group of plants. The 

 mean flower-size for spread of flowers, of the Fa-plant from which 

 this F^population was derived was 24.89 mm, while the mean 

 corolla spread of the 51 Fg-plants was 27.43 mm. The ränge of this 

 F^-population for spread of flowers was not as great as the ränge 

 of the 17 F.i-plants of the previous year, though it is approximately 

 the same so far as the limits of the ränge are concerned. The 

 mean of 27.43 mm, is approximately the same as the 1913 Fo mean 

 of 27.59 mm. It is entirely possible that of many other Fg-families 

 some might have showa significant diff"erentation but the relativdly 

 few measurements made upon three other Fg-families showed in 

 general a ränge corresponding to that of the one F3 measured 

 extensively. The ränge of this Fg with reference to lenght of corolla 

 tube shows an extraordinary extent, yet the mean is approximately 

 the same as the mean between the parents. 



M. J. Sirks (Haarlem). 



Tschermak, E. von, Ueber die Vererbungsweise 



von 



