re. 
PHYSIOLOGICAL STIMULI AND ITS SIGNIFICANCE 25 
The differences mentioned between the haploid and the diploid pollen- 
grains of the hyacinth are not directly comparable with those of Oeno- 
thera. The normal diploid varieties of Hyacinthus have ellipsoidal nor- 
mal haploid pollen, while the abnormal diploid grains are very large and 
globular in shape. Among such heteroploid varieties as Totula (30 chro- 
mosomes in the somatic cells), doubtless pollengrains with nuclei con- 
taining 16 chromosomes, which together have the same size as the 16 
chromosomes of the pollennuclei of the diploid varieties will be formed 
under normal conditions. Still such normal generative nuclei with 16 
chromosomes of Totula and other heteroploid varieties are not globular 
but ellipsoidal in shape. Compare also what will be said below about 
SAKAMURA’s investigation (1920). BUCHHOLZ and BLAKESLEE (1922 p. 
2), have found, that in the case of Datura normal pollen has a greater 
fertilisation-power than pollen with an aberrant number of chromo- 
somes. 
HERIBERT-NILSSON (1920) distinguishes „morphologically’ different 
kinds of pollen and states that the rate of growth of the pollentubes 
depends on the temperature, while those of O. Lamarckiana grow more 
rapidly than those of Oenothera Lamarckiana gigas. All these facts pro- 
bably form the reason, why the number of triploid seedlings, arising from 
diploid parents, is so small under „normal’ conditions. 
Even, after pollination with plurinuclear pollengrains, fusion of but 
one haploid nucleus with the eggcell is very well possible. 
Through what I have observed about the formation of the seed of the 
hyacinth, the possibility does not appear to be excluded, that the en- 
dosperm can reach a higher degree of pluriploidy than triploidy, in 
other words, that either a diploid spermnucleus or several haploid glo- 
bular nuclei can fuse with the endospermnucleus. Such might especial- 
ly have been the case in the seed which was formed after selfing Yel- 
low Hammer abn. W., and which, after very slow growth, reached such 
a strikingly large size. In the spring of 1922 the seedcoat only of this 
seed remained. No embryo had been formed. Whether in this way seeds 
without embryo’s can be formed must be investigated and also the 
question, in how far a swelling of the ovaria after selfing may be due 
to the formation of endosperm without eggcell-fertilisation. 
The observations of Heribert Nilsson (1922) tend to consider the pos- : 
sibility that after pollination, the tubes of the normal haploid pollen- 
grains may grow more rapidly than those of the plurinuclear ones, in 
