264 DUPLICATION OF GENERATIVE NUCLEI BY MEANS OF 
in which the leaves have not been removed from the Oenothera plants, 
the sowing of the seeds in the hot-house, early in the year, when the 
intensity of the light is still light, may have had its effects. 
May we conclude from this, that the formation of diploid gametes, is due 
to physiological stimuli e.g. to external conditions, not only in the case of 
Hyacinthus but also in that of Oenothera and other biannual and peren- 
nial Phanerogams, among which pluriploid plants have arisen from di- 
ploid ones, as in the cases of Allium, Canna, Chrysanthemum, Dahlia, 
Hieracium, Morus, Musa, Narcissus, Primula and others? 
No doubt reflection on this question, is of great importance, both for the 
further solution of the evolution-problem and for the amelioration of our cul- 
tivated plants. In this connexion I should like to call attention to BLa- 
KESLEE'S (1922, p. 31) words, put as a motto at the head of this article. 
No doubt, also, that on the solution of this question, the discovery 
depends of the method to be followed to force annual plants to the pro- 
duction of fertile diploid generative nuclei or to that of pollengrains 
with several haploid sexual nuclei. The discovery of pluriploidy in the 
case of annual plants, such as Datura by BLAKESLEE and his assistants, 
and also — according to my judgement — the origin of diploid pollen- 
grains of Vicia Faba by external stimuli (Cf. SAKAMURA 1920 p. 145 
fig. 23 and Chapter III) leads us to this prediction. It cannot be denied, 
moreover, that the obtention of diploid sexual nuclei by means of phy- 
siological stimuli, approaches more nearly the opinion that crossing be 
the cause of the splitting of chromosomes in the zygote (BREMER 1921, 
p- 108) than the opinion that such sexual nuclei owe their origin to mu- 
tation, in the sense of DE VRIES. 
Probably Lotsy’s words (Genetica III) p. 455 will, in connexion with 
the subject treated, gain in force in the near future: „I Should like to 
be allowed to ask those, who defend the existence of transmittable va- 
riability, whether they do not agree with me, that such akind of varia- 
bility, if it does exist, must in the last instance be caused by exter- 
nal stimuli?” If then, really, the origin of pluriploid sexual cells and 
the explosive appearance of various heteroploid hybrids,which is doubt- 
less connected with it, is caused by circumstances, for the greater part 
at least foreign to the nature of the organism, we may well ask whether 
such terms as „mutation-period”, „mutation-coëfficient”, „parallel- 
mutation”, „progressive mutation”, used in the sense of DE VRIES, can 
any longer be maintained! 
