AND SPECIES-HYBRIDS WITHIN THE GENUS SACCHARUM 319 
As to the way, in which higher chromosomenumbers, arise from lower 
ones, opinions differ greatly. 
STRASBURGER 2) was of opinion, that doubling of the number of chro- 
mosomes could take place by longitudinal fission of all chromosomes 
during a karyokinesis, in which the division is not completed, so that 
one tetraploid nucleus results in stead of two diploid daughternuclei. 
He was also of opinion, that possibly two daughternuclei resulted at 
first, but that these subsequently reunited. He deemed it probable, 
that it was the fertilised eggcell in which such a chromosome-increase 
should occur. As a second cause of the origin of chromosomenumbers, 
a multiple of other chromosomenumbers, STRASBURGER was of opinion 
that transverse division of chromosomes should be accepted. This 
would, simultaneously with the increase in number, cause a decrease in 
the size of the chromosomes themselves. Chromosome-increase by lon- 
gitidunal fission should lead to the formation of nuclei of greater size, 
while in the case of increase of the number of chromosomes by trans- 
verse division the size of the nucleus would remain unchanged. 
ROSENBERG 8) says — in my opinion rightly, about the origin of 
Hieracium-species with a higher chromosomenumber from such with 
a lower number: 
„Wo die Chromosomenzahl einer Art ein Vielfaches einer anderen 
derselben Gattung ist, wie in den oben angeführten Fällen, ist wohl 
eine Entstehungsweise durch Quersegmentierung von Chromosomen 
unwahrscheinlich”. 
As to the origin of the tetraploid chromosomenumber of Oenothera 
gigas, GATES !) is of opinion that the increase must have taken place 
after fertilisation had occurred. This doubling would have taken place 
in the zygote by means of longitudinal fission of the chromosomes, not 
immediately followed by cell-division. STOMPS ?), to the contrary, is of 
opinion, that Oenothera gigas has arisen from the union of two gametes 
„both of which contain, as a consequence of mutation, a double num- 
ber of chromosomes in their nuclei.” 
2) E. STRASBURGER. Chromosomenzahl. Flora 100. 1910. 
3) O. ROSENBERG. Die Reduktionsteilung und ihre Degeneration in Hieracrum 
Svensk Botanisk Tidskrift. Bd. 11. 1917, p. 196.. 
1) R. R. Gates. The Behaviour of the Chromosomes in Oenothera lata x O. 
gigas. Bot. Gazette 48. 1919, note, p. 196. 
2) Tu. J. Stomps. Kerndeeling en Synapsis bij Spinacia oleracea L. Disser- 
tatie 1910, p. 58. | 
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