314 A CYTOLOGICAL INVESTIGATION OF SOME SPECIES 
x O. gigas) she found very different chromosome numbers, which 
points to a different behaviour of the univalent chromosomes in this 
respect, that they sometimes are included in the tetrad-nuclei while at 
other times they are not. 
Already in the first generation of the cross O. lata X O. gigas she 
found among 52 individuals the following chromosome-numbers 
“number of chromosomes. : . . 15 21 22 23 29 30 
number of individuals: „nnen 1.022 16 20 3 2 4 
The chromosome-number 15 could, in her opinion, be explained by 
apogamous development of a non-reduced gamete, the numbers 29 and 
30(?) by fertilisation of a non-reduced female gamete by a reduced 
male one. 
Miss LUTZ consequently found that from the cross O. lata x O. gigas 
hybrid individuals can arise, which possess a chromosomenumber ex- 
ceeding that of the sum of the haploid chromosomenumber of the pa- 
rents. This, she imagined, to be caused by the fertilisation of a diploid 
gamete of the one parent-species by a haploid one of the other in the 
formation of the individuals in question. 
STOMPS ') could show the same in the case of individuals of the so 
called Oenothera hybrida Hero. These individuals have 21 chromosomes 
in their vegatative nuclei and arose from crosses of species with ha- 
ploid 7 chromosomes. According to STOMPS 2) these arose from the fu- 
sion of a normal gamete with one, which, in consequence of gigas- 
mutation, possessed a doubled chromosome-number. 
Forms, containing during the division of the gonotokonts univalent 
chromosomes besides bivalent ones, have furthermore been found by 
TACKHOLM 3) in the genus Rosa. Besides species, which during diakine- 
sis possess 7, 14 and 21 chromosome-pairs, there are others, which 
besides 7 bivalent chromosomes, have 7, 14, 21 and 28 univalent ones, 
all of the later should be considered as hybrids between ‘species 
with different chromosomenumbers. TACKHOLM found moreover, that 
in the case of roses, which reproduce themselves in an apogamic way, 
1) Tu. J. Stomps, Die Entstehung von Oenothera gigas. Ber. D. Bot. Ges. 
Bds30s 1912: 
2) Tu. J. Stomps. Ueber den Zusammenhang zwischen Statur und Chromo- 
somenzahl bei den Oenotheren. Biol. CBI. 1916, p. 157. 
3) G. TÄCKHOLM. On the Cytology of the Genus Rosa. A preliminary note. 
Svensk. Bot. Tidskr. 1920, p. 300. 
Se eo 
