SPECIES HYBRIDIZATION 247 
when lamarckiana is crossed with rubrinervis, the rubrinervis pangen in 
lamarckiana is in the labile condition, but in rubrinervis it is in the in- 
active condition. Here, however, a difficulty is introduced by the fact 
that the form corresponding to rubrinervis in F, is intermediate between 
rubrinervis and lamarckiana, it is the form which de Vries calls sub- 
robusta. Must we assume a fourth condition for the pangens in this 
form? An additional difficulty is introduced when we consider crosses 
of rubrinervis and nanella. Rubrinervis has arisen from lamarckiana 
by mutation, by a change of the labile rubrinervis pangen in lamarckiana 
into the inactive condition. But when rubrinervis is crossed with nanella, 
F, consists entirely of lamarckiana and subrobusta plants. As we pointed 
out, crosses of nanella with lamarckiana show that the nanella pangen 
NN x nn 
rubrinervis Se 
N'N' Nn 
lamarckiana subrobusta 
| ape SS ea oe 
N'N' NN Nn nn 
lamarckiana rubrinervis subrobusta nanella 
Fig. 105.—Results of crossing two ‘“‘mutants”’ of Ginothera lamarckiana. 
in lamarckiana is in the labile condition. How, then, should this 
pangen have become inactive in rubrinervis which was supposedly de- 
rived from lamarckiana by a change in the rubrinervis pangen? For 
according to de Vries the behavior of the nanella pangen in such an 
experiment is illustrated in Fig. 105 in which the active pangen 
is designated by N, the labile pangen by N’, and the inactive pangen 
by n. 
Those who have attempted to apply a rigid Mendelian analysis to the 
Cnothera phenomena have failed to do so without making assumptions 
which thus far remain beyond the limits of experimental verification. 
Nevertheless the work of such investigators as Heribert-Nilsson, Renner, 
Davis, and others demonstrates that Mendelian analyses may be applied 
to particular cases and that when the difficulties which occur in Ginothera 
are considered, the facts thus far discovered do not preclude an ex- 
planation on an essentially Mendelian basis. Davis in particular has 
pointed out that thus far no species of Ginothera has been found which 
will stand trial as of strict genetic purity. In all species apparently 
50 per cent. or more of the pollen grains are abortive and similar 
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