McAllister—Cytology and Embryology. 607 
somes and the latter with 20, found that in late prophases of 
the heterotypic division of the pollen mother cells ten double 
chromosomes and ten unpaired single chromosomes were present. 
Rosenberg explains this distribution by assuming that the ten 
paternal chromosomes pair with ten from the maternal parent, 
thus leaving ten female chromosomes unpaired. Unfortunately 
these hybrids do not set fertile seed, so their conduct during the 
reduction divisions in succeeding generations could not be 
traced. 
Gates (30) has reported, on the other hand, that hybrids of 
Oenothera lata X O. gigas, the former with 14 and the latter 
with 28 somatic chromosomes, show in th© diakinesis and meta- 
phases of the first reduction division, 21 chromosomes which 
give little or no evidence of pairing. In the heterotypic di¬ 
vision these 21 chromosomes are distributed as nearly equally 
as possible between the daughter nuclei, one getting eleven and 
the other getting ten chromosomes. 
Strasburger (100), commenting on Gates’ observations, is of 
the opinion that the single equatorial plate stage which Gates 
has figured and which Strasburger has reproduced in his plate 
might easily be conceived to show seven single and the seven 
pairs of chromosomes,—with a single member of a pair lacking, 
which, according to the theory of the pairing or homologous 
chromosomes, should be present. Still, such pairing as is shown 
in this figure does not go far, to say the least, in establishing 
any theory of the pairing of homologous chromosomes. 
There seems thus to be considerable evidence that there is a 
pairing and conjugation, more or less intimate, of the paternal 
and maternal chromosomes, occurring during or shortly before 
the prophases of the first reduction division. But in regard to 
the question as to how the chromosomes are paired there is a 
marked difference of opinion. Allen, Gregoire, Strasburger 
and others have interpreted the phenomena as showing pairing 
of chromosomes side by side, while Farmer and Moore, Mottier 
and others believe the pairing of the parental chromosomes to be 
end to end. 
