316 G@NOTHERA AND THE MUTATION THEORY 
An application of the principle of balanced lethals 
to O. Lamarckiana indicates that the chromosome 
pair that contains the balanced zygotic lethals (7.e., 
that is responsible for the differences between leta 
and velutina) is the one that is most important in 
the production of the “mutant” types. It is 
apparently in this pair of chromosomes that nanella, 
oblonga, rubrinervis, blandina, simplex, erythrina, 
and others differ from typical Lamarckiana. If we 
regard Lamarckiana itself as heterozygous and write 
leta 
its formula ———— 
velutina 
it is possible to write similar 
formule for the other types named, as has been 
done in a slightly different fashion by deVries 
himself. The ‘‘leta”’ and “velutina”’ are not to be 
thought of as single allelomorphs, but rather as 
whole homologous chromosomes that differ in a 
number of genes. In the formule below the other 
terms may be thought of as follows: 
oblonga — mostly leta, but modified either by crossing over 
or by mutation. 
deserens — like leta in most respects. 
decipiens — also like leta. Differs from deserens only in not 
having a gene for brittleness. 
blandina — smooth leaved; otherwise like velutina. 
None of these, except oblonga, carries a lethal; the 
lethals have presumably been lost by crossing over. 
The terms just given apply to the chromosomes; 
the plants themselves may be represented as follows: 
