254 DUPLICATION OF GENERATIVE NUCLEI OF MEANS OF 
It may be assumed that hybridisation may cause the origin of varie- 
ties possessung a greater susceptibility to the physiological stimuli dis- 
cussed, than others. This does not mean, that duplication of generative 
nuclei can happen in the case of heterozygous plants only. It may be assu- 
med that it can be caused equally well in the case of homozygous ones. 
The conclusion of TISCHLER (1809 résumé) that „die Unregelmässigkei- 
ten bei der Tetradenteilung nicht als Characterismus der Bastardnatur 
betrachtet werden dürfen’ and the experiments of NEMEC (1910, p. 
192—193) with Larix decidua — irregular chromosome distribution, 
formation. of gigantic pollengrains, non-formation of divisionwalls be- 
tween generative nuclei —, support this opinion. 
Consequently our insight in the nature of dominance and recessive- 
ness may be increased. We may become able to compare heterozygous 
descendants, formed by the fusion of 2 haploid sexual nuclei, with 
others, originated by the fusion of a diploid and a haploid sexual nu- 
cleus, both with the same qualities as the former. This will allow us to 
decide whether, and, if so, to which extent, a double dose of the same gens 
modifies that, which normally dominates or is recessive. 
IX. DOES THE CAUSE OF THE ORIGIN OF THE EXPERIMENTALLY 
OBTAINED TRIPLOID PROGENY CORRESPOND WITH THAT OF 
THE ORIGIN OF THE TRIPLOID VARIETIES OF HYACINTHUS 
ORIENTALIS, WHICH APPEARED IN THE DUTCH 
CULTIVATIONS ? 
1°. Ripe, germinable, pollengrains with duplicate generative nuclei ha- 
ve been obtained by exposing the young flowerbud to abnormal 
external conditions; 
2°. after pollination with pollen in which these abnormal pollengrains 
were in the majority, triploid descendants have been obtained. 
These were the two chief-results of the experiments. 
If we now fix our attention on the practical cultivation of the Dutch 
Hyacinths, we find: 
1°. that in those cultivations the abnormal fertile pollengrains occur 
also (Cf. the Introduction) ; 
2°. that in those, also, repeatedly, triploid plants have been obtained. 
The first of these facts was recorded in publication 19215; the se- 
cond in 19204 and 6 and in 19214. 
