ER TT a eee ee ee Re, Oe et 2 aves) ee? ee) ea ws Cee, 
BSEe, ree IPE ego mee Rae Ae Phe ey 
re OM RET CVE S See ea oh ho PP ee, Se ee Ae ee Ps ee epee hemot, Wp 
a, Fran we ee as ee ae ‘eet eet ae i 
1909] GATES—-CHROMOSOMES IN OENOTHERA 195 
has arisen through a disturbance by some means of this delicate con- 
dition of balance. 5 
But it is useless to speculate on such possibilities until it is known 
_ whether the chromosomes of Oenothera are really unlike, and at 
present there is no evidence in favor of this view except the inferential 
evidence from chromosomes in general. The fact that chromo- 
somes reappear with each mitosis, showing the same differences 
where visible differences exist (except in the cases of amitosis, whose 
_ Status in relation to hereditary processes is not at present understood), 
_ would seem to favor the assumption that they maintain their identity 
_ and are unlike. But I need not cite here the general arguments in 
_ favor of this hypothesis. ‘The more definite evidence, such as that of 
the sex chromosomes in insects, is not necessarily of universal applica- 
tion. 
SUMMARY 
1. O. lataXO. gigas has 21 chromosomes in its somatic cells, 7 of 
maternal origin (O. /atd) and 14 of paternal origin (O. gigas). In 
one individual the number was 20, owing probably to the absence 
_ of one chromosome from one of the germ cells which produced this 
individual. 
2. These chromosomes segregate at the time of reduction, so that 
in individuals having 21 chromosomes half the germ cells receive 10 
and half 11 chromosomes. In the individual having 20 chromosomes, 
Io enter each germ cell. Occasionally one chromosome goes to the 
_ Wrong pole of the spindle, so that in plants having 21 chromosomes 
a few germ cells are found having 9 or 12 chromosomes and in the 
plant with 20 chromosomes, occasional germ cells have 9 or 11 
Rade etre Mipkyes 8 
} ion accounts 
chromosomes. This irregularity in d 
for the fact that different individuals in a race in some cases have 
different numbers of chromosomes. 
3. The 10-11 segregation of chromosomes in the formation of the 
8erm cells of this hybrid shows that there is not here a pairing and 
S€paration of homologous chromosomes of maternal and paternal 
Origin, but that the segregation tends to be into two numerically 
_ €qual groups. 
Bir 
ee 
~< 
4. Evidence from this and other work shows that there are two 
general methods of chromosome reduction in plants, one involving 
