PHYSIOLOGICAL STIMULI AND ITS SIGNIFICANCE 261 
terial bearers of heredity. This happens in the so called gigas-muta- 
tions, which have been observed in Oenothera Lamarckiana, O. grandi- 
flora, O. pratincola and O. stenomeres. In other cases the number of 
chromosomes increases by one, as in the mutants, lata, scintillans and 
others. That these cases can not be explained through the loss of a cha- 
racter or as the reappearance of a quality of earlier ancestors, is adnut- 
ted by most authors. They must therefore be considered to be progres- 
sive. But, as I have said already, we do not yet dispose of a conclusive 
and convincing criterium’. 
Morea (Lc. p. 149) says: „The way in which gigas originates has 
been much discussed, but no conclusion reached’. 
WINKLER (l.c. p. 158): „Wie die , triploide’’ Chromosomenzahl zu er- 
klären ist, bleibt dahin gestellt und muss in jedem einzelnen Falle be- 
sonders untersucht werden”. 
The opinions offered as to the cause of origin, are very diverse in na- 
ture. They are chiefly based upon considerations in connexion with the 
appearance of triploidy in Wikstroemia, Oenothera, H teracium and Pri- 
mula. 
We may resume them as follows. : 
1°. Doubling of the chromosomes by longitudinal splitting must have 
occured during the first stages of the formation of the embryo e.g. 
after the formation of the zygote (GATES 1909, STRASBURGER 1910, 
Davis 1911, ERNST 1918.) 
2°. The cause lies, in the first instance, in the occurrence of diploid ga- 
metes (SToMPS 1912, 1916; DE VRIES 1913, 1915; VAN OVEREEM 
1920.) It may be remembered here that GEERTS (1909 p. 144) found 
28 chromosomes, in stead of 14 in a pollenmothercell of Oenothera 
Lamarckiana. 
Doubtless, the opinion of some other authors is influenced by the 
opinion on the causes of evolution, which they foster. 
It is therefore easily understood —- to take a few expressions of opi- 
nion among the many put forward — why ERNST writes (l.c. p. 356): 
„Nichts scheint mir nun näher zu liegen, als den Anstoss für die Abnor- 
mität der Keimkernbildung und -teilung gegeben zu sehen im heterogenen 
Character der zu Vereinigung kommenden Gameten-kerne. It is however 
equally acceptable, that WINKLER (1920 p. 150 and 158) opposes 
ERNST in this question, e.g. does not consider crossing as the cause, and 
that Morcan (1919) says about the origin of Primula Kewensis : 
