262 DUPLICATION OF GENERATIVE NUCLEI BY MEANS OF 
, What connexion there may have been between hybridisation and 
the subsequent doubling, if there is any connection, is by no means 
clear.” 
Chiefly then: hybridisation as the cause of pluriploidy versus muta- 
tion. (Cf. DE VRIES (1918, p. 16): „The internal causes of mutations are 
of quite another nature” (e.g. as those of segregation and the opinions 
‚referred to above). 
It will be understood, that we are inclined, on the ground of the facts 
established in the case of Hyacinthus orientalis, to add to the 6 points of 
more or less complete similarity between the cytological-hereditary 
phenomena observed among the Oenothera’s and Hyacinthus orientalis, 
a 7th one, to wit: 
DUPLICATION OF GENERATIVE NUCLEI PRECEEDS THE ORIGIN OF PLU- 
RIPLOID FORMS FROM DIPLOID ONES, BOTH IN THE CASE OF Oenothera 
AND IN THAT OF Hyacinthus orientalis. 
This forces us, to put the very important question: what is the cause 
of that duplication of generative nuclei ? 
Is this cause an internal one? Is it only present in the case of orga- 
nisms, which , mutate’ in the sense of DE VRIES? Or can external cir- 
cumstances force all hybrids, or even all organisms, homozygous ones 
as well, which in normal cases are able to form normal haploid genera- 
tive nuclei, to form diploid ones? 
Hyacinthus orientalis certainly shows that the formation of duplicate 
generative nuclei is not limited to , mutating’’ organisms, so that there 
is considerable reason to believe that, in hybrid plants at least, exter- 
nal circumstances are able to cause duplication of generative nuclei. 
It must here he pointed out, that DE VRIES does not entirely exclude 
the influence of external circumstances on the production of pluriploid 
Oenothera’s. After having said that the coefficient of mutation of Oeno- 
thera gigas is 0.0009 %, while it had previously and preliminary been 
estimated at 0.01, he adds in a note: 
„Es sei hier daran erinnert, dass die Mutationskoeffizienten keines- 
wegs konstante Zahlen, sondern innerhalb gewisser Grenzen van aüs- 
seren Einflüssen abhängig sind”. We need not say, that DE VRIES con- 
tinues to consider Oenothera gigas as a progressive mutant. 
We have repeatedly pointed out, that the duplication of the gene- 
rative nuclei of the hyacinth is chiefly caused by the early harvesting of 
the bulbs in an unripe condition. What this means for the young bud, 
NT 
