146 DISTRIBUTION OF THE CHROMOSOMES 



ever, no data concerning the genetic behavior of the 

 hybrids have been reported. 



Another instance of parallehsm between unusual 

 chromosome phenomena and genetic results is that 

 found in QEnothera lata and semilata by Lutz, Gates 

 and Thomas. The normal chromosome number in 

 QEnothera lamarckiana is 14, but the race called lata 

 always has 15 chromosomes, i.e., one kind of chromo- 

 some exists in the triploid number. This is true 

 even of lata plants which originated independently 

 of the ordinary stock, in widely different races of 

 GEnothera. The same results apply to semilata, 

 which appears to be a variety of lata. Lata and semi- 

 lata occasionally arise '' spontaneously " from lamarck- 

 iana, in a small per cent, of the offspring of any one 

 individual, and the explanation for this may be found 

 in the fact that occasionally, in the gametogenesis 

 of lamarckiana, two mated chromosomes, instead of 

 separating, pass to the same pole (non-disjunction) 

 so that the offspring would have three chromosomes of 

 this type and contain 15 chromosomes in all. The 

 behavior of the extra chromosome in the lata indi- 

 viduals is also of interest, for it is found that in 

 gametogenesis, w^hen the mated chromosomes sepa- 

 rate, the extra chromosome does not divide regularly 

 as do unpaired chromosomes in moths, but tends to 

 pass to one pole. This would result in half the 

 gametes containing it and transmitting the lata con- 

 dition and the other half being normal. Very often, 

 however, the chromosome lags on the spindle and 

 so fails to be included in the nucleus of either daughter 



