441 



If this were the case we should more frequently meet with homo- 

 zygotic pairs of parents, to whom would consequently belong a 

 group of children with very slight differences of the indices. These 

 however do not occur in the lists. Tlie Table which contains the 

 families with four grandparents of which consequently three com- 

 plete generations are known furnishes moreover the indubitable proof 

 that the headform is not inheritable on account of a single pair 

 of allomorphic factors. 



Consequently we reject the indication of the motion of heredity 

 according to the monohybridic scheme. 



It is very well possible that inheritance of the headform is deter- 

 mined by a progression of units. Heredity goes then according to a 

 type that Ntlsson-Ehle ^) (1909 — 1911) has systematically worked 

 out for cereals and that according to different investigators (Lang, 

 T. Tammes a.o.) may be applied to their results. If the head form 

 in the conception of Nilsson-Ehle is determined by a few pairs of 

 units, consequently A^A^A^ . . . and a^a^a^ . . . then of a pair of 

 parents, the father can possess a factor of heredity that the mother 

 misses, and the reverse, or in heterozygotic form. Among the children 

 may then, by combination of factors, occur headforms with indices 

 larger, resp. smaller, than those of the parents. Generally a great 

 variability is to be observed with mutually slight differences, which 

 in a restricted number of individuals may give the impression of 

 intermediary heredity. By special combinations which, as can easily 

 be calculated, are very rare, greater deviations may occur. By a 

 separate breeding of the third bastard-generation (i^,) it can be 

 proved that a cross-breeding follows this scheme. Then different 

 proportions of number must occur, according to the number of 

 Mendelian factors which has been adopted for the explanation of 

 the second bastard-generation. This took indeed place in Nilsson- 

 Ehle's experiments. 



The data of different families plead for the fact, that, if the 

 heredity of the headform follows the rules of segregation of Menuel, 

 factors working in the same direction in the sense of Nilsson- 

 Ehle must be admitted. So e. g. those, that have been gathered in 

 table VI, where one index deviates considerably from the others. 

 Likewise those of table VII, where the indices of the children 

 surpass those of the parents on both sides or on one side. 



We find consequently in the collected material indications for the 



1) H. Nilsson-Ehle. Kreuzungsuntersuchungen an Hafer und Weizen. I und 11» 

 1909 u. 1911. Acta Üniversitatis Lundensis Lund. 



29 

 Proceedings Royal Acad. Amsterdam. Vol. XX. 



