CNOTHERA AND THE MUTATION THEORY 317 
oblonga : ._ deserens 
oblonga = - rubrinervis = ———— 
velutina velutina 
‘ deserens decipiens 
lucida = or 
leta leta 
deserens decipi 
deserens = — erythrina = es 
deserens velutina 
decipiens blandina 
decipiens = = blandina = : 
ae decipiens anne blandina 
. leta (minus the lethal) 
simplex = 
leta, 
There is apparently normally a gene for dwarfness 
in the leta chromosome, and the appearance of 
nanella is due to this gene crossing over from most 
of the rest of the complex to give a chromosome that 
is velutina plus dwarfness. This chromosome, if at 
fertilization it enters the same zygote as a normal 
leta chromosome, will give rise to a dwarf that is 
still in the balanced lethal condition and that will 
react in most respects like Lamarckiana itself. 
It seems very probable that the differences be- 
tween most of the chromosomes in these mutant 
types are due to their being the results of crossing 
over at different levels. They are simply mixtures 
of the original leta and velutina chromosomes in 
different proportions. DeVries, however, believes 
that all of the differences between them are due to 
mutation rather than to crossing over, and it may 
well be that some of them are of this nature. It is 
not yet possible to construct a map of this chromo- 
some that will explain the observed results con- 
sistently. Shull has recently given a preliminary 
