260 DUPLICATION OF GENERATIVE NUCLEI BY MEANS OF 
4°. In regard to the degree of fertility of the generative cells, many 
phenomena observed in the case of Hyacinthus orientalis, are the 
same as those in the case of Oenothera. 
5°. A certain correlation between the number of chromosomes and the 
habit of the plant occurs both in the case of Hyacinthus orientalis and 
in that of Oenothera, both also show clearly, that the connexion be- 
tween the number of chromosomes or the volume or the size of the 
surface of the nucleus on the one side and the size of the cells or the 
number of the cells or the habit, on the other side, is not of a merely 
mechanical nature. 
6°. The origin and the nature of nanella-forms ofOenothera also reminds 
us, to a certain extent, of the formation of dwarf-forms of hyacinths. 
In connexion with the present standpoint of the evolution-problem, 
two points in the conduct of Oenothera and Hyacinthus orientalis, are of 
special importance: 
1°. the sudden origin of triploid forms from diploid ones, 
2°. the greater frequency of the triploid ones, 
because, a comparison of the way in which different investigators IMA- 
GINE these phenomena to have been caused in the case of Oenothera with 
the cause, suggested by de Hyacinthus-EXPERIMENTS, may lead to im- 
portant consequences. 
It is sufficiently known, that so far the cause of the origin of pluri- 
ploid Phanerogamia has remained obscure: 
No wonder, when ERNST could still write in 1918 on p. 360 of his 
book: . 
„Die experimentelle Erzeugung von triploiden und ditriploiden Ras- 
sen durch experimentelle Dispermie wie diejenige triploider und ditri- 
ploider Bastarde dürfte zum mindesten denselben Schwierigkeiten be- 
gegnen und eine ebenso umfassende Versuchsanstellung notwendig ma- 
chen, wie diejenige der gigas und semi-gigas-Formen der Oenotheren 
nach den Berechnungen van DE VRIES und STOMPs.”’ 
_ The uncertainly of the final cause is also pointed out by DE VRIES 
(1918), MORGAN (1919) and WINKLER (1920). 
On p. 11 DE VRIES writes: „I now come to the discussion of the pro- 
gressive mutants; they are extremely rare in Nature and consequently 
in our cultures also.” Referring to the characters of progressive mu- 
tants, DE VRIES says (l.c. p. 17): „The most important are the doubling 
of the number of chromosomes in the nuclei of the cells e.g. of the ma- 
