— ders Bl 
PHYSIOLOGICAL STIMULI AND ITS SIGNIFICANCE 267 
Narcissi, which are now cultivated, have originated in a correspon- 
ding manner. 
15. A study of the litterature shows, that the possibility of duplica- 
16. 
tion of sexual nuclei need not be limited to Monocotyledons. 
It is therefore the more necessary, to enquire whether in the case 
of the Oenothera’s the method under which these are usually cul- 
tivated — shortening of the vegetative period — is not responsible 
for the origin of pluriploid forms among them, as a consequence of 
the duplication of sexual nuclei by means of physiological stimuli. 
