KFFKCTS OF AMPHIMIXIS ON ONTOGENY 26 1 



of idants. 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 constancy of the specific characters 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 amphimixis, and each group of them may be 

 assumed to consist of s//////ar ida.nts. 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 these com- 

 binations of characters may be divided into three principal 

 groups, viz. : — (i) a ijieaii between both parents is 7)iaintained 

 in all pai'ts of tJie plaiit ; (2) t/ie cliaraderistics of the father or 

 7?iother predojni?iate ; and (3) certain parts of the hybrid exhibit 

 the maternal, and others tJie paternaL characters. 



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

 may take as an example the hybrid obtained by KoUreutter from 

 two species of the tobacco plant, — Nicotiana rnstica 9 and TV. 

 paniculata $ . KoUreutter 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 iV". panicn- 

 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. rnstica 

 is 14 mm. long, that oi 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 KoUreutter, ' Vorlaufige Nachricht von einigen das 

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



