EFFECTS OF AMPHIMIXIS ON ONTOGENY 26 1 



of iciants. The extent to which the determinants of any indi- 

 vidual character are represented — whether they are contained in 

 all the ids, or only in a small portion of them — could only be 

 ascertained from the phenomena of heredity if we knew tie 

 cause of the predominance of any particular ' successful " charac- 

 ter. This, however, can only be inferred from crosses between 

 species, the great constanc\' of the specific cliaracters in which 

 leads us to presuppose that their determinants predominate in all 

 the idants of the parental germ-cell. 



In plant-hybrids, paternal and maternal idants come together 

 in the process of amphimi.xis. and each group of them may be 

 as.sumed to consist of w////(^?;' idants. The effect this arrange- 

 ment will produce on the phenomena of heredity must now be 

 considered, and conclusions drawn from these considerations. 



From a very large number of observations on hybrid-plants, 

 we find that, in the first place, parental characters may be 

 variously intermingled. From a comparison of all the cases 

 observed up to the year 1881. Focke * concludes that the.se com- 

 binations of characters may be divided into three principal 

 groups, viz. : — (i) a mean between both parents is maintained 

 in all parts of the plant ; (2) the characteristics of the father or 

 mother predominate ; and (3) certain parts of the hybrid exhibit 

 the maternal, and others the paternal, characters. 



The first-mentioned case is by far the most frequent : we 

 may take as an example the hybrid obtained by Kollreutter from 

 two species of the tobacco plant, — Nicotiana rustica 9 and N. 

 paniculata $ . Kollreutter f himself stated that this plant was 

 exactly intermediate between its parents, while it was considered 

 by Gartner to bear a slightly greater resemblance to A\ panicu- 

 lata, and by Focke to N. rustica. Kollreutter's opinion is probably 

 therefore a fairly accurate one, for in any case the point can 

 only be estimated, and cannot be decided with mathematical 

 precision. According to Focke. the corolla-tube of N. rustica 

 is 14 mm. long, that o{ N. paniculata 26 mm., and that of the 

 hybrid 19 mm. The exact mathematical mean between these is 

 20 mm. ; and hence in this character the hybrid approaches N'. 

 paniculata. As regards the diameter of the widest part of the 



* ' Die Pflanzen-Mischlingen,' Berlin, 1881. 



t Joseph Gottlieb Kollreutter, ' Vorlaufige Nachricht von einigen das 

 Geschlecht der Pflanzen betreffenden Versuchen u. Beobachtungen," 1716. 



