348 PERMANENT HYBRIDS 



should consist of two complexes, one unchanged velans, the other a 

 mixture of velans and gaudens. This is in agreement with the 

 conclusions of the geneticist [cf. Hoeppener and Renner, 1929) who 

 describes the two as " pcenevelans " and " subpelans." Pcenevelans 

 is the velans complex derived normally from Lamar ckiana ; the 

 slight difference it shows in later generations from the velans of the 

 parental form is probably due to crossing-over in the half-mutant 

 with suhvelans. This mutant yields one-quarter bad seeds, one-half 

 seedlings like itself with the same chromosome configuration, and 

 one-quarter suhvelans. suhvelans, which is the " full -mutant " 

 CE. deserens. This form, being homozygous, has seven pairs of 

 chromosomes (7(2) ) at meiosis. It arises, we may say, because 

 suhvelans no longer includes the chromosomes with the lethal factors 

 of velans. Emerson (1936) has described genetical evidence of the 

 same kind of process in CE. pratincola. 



Segmental interchange between chromosomes of the same 

 complex will have a different result, for the seedlings, whose parental 

 gametes have suffered the change, will not differ in appearance from 

 their parents, but their chromosomes will pair differently. Where 

 the parents had a ring of 14 chromosomes the seedlings will have 

 two rings, (12) + (2) or (10) + (4) or (8) -f (6). Now the rule that 

 plants with the multiple ring breed true to this character need not 

 apply equally to the small rings derived from it. CE. hiennis 

 ( (8) -f- (6) ) breeds true because, presumably, each ring is preserved 

 by its lethal system ; but where one ring is broken into two by 

 interchange each half will not necessarily have its lethal system. A 

 new ring of four chromosomes in a plant from two gametes, one of 

 them with chromosomes AB and CD the other with chromosomes 

 BC and DA, may yield homozygous progeny either of the type 

 AB-AB, CD-CD or the type BC-BC, DA-DA if either of these is 

 viable [i.e., has no factors lethal in the homozygous condition). 

 Hence a plant whose parental gametes have undergone interchange 

 between chromosomes of the same complex may be expected to 

 yield progeny homozygous in regard to the members of one of the 

 small derived rings in high proportions by a process which is 

 essentially one of mendelian segregation. Such is a possible 

 explanation of the origin of '* mass-mutation " in CE. Reynoldsii 



