Unisexual Crosses 263 



them has as yet not been made. Unfortunately 

 many of the better systematists are in the habit 

 of throwing all these interesting forms to- 

 gether, and of omitting their descriptive study. 

 I have performed a large number of crosses 

 between such undescribed types and as a rule 

 got constant hybrid races. Only one or two 

 exceptions could be quoted, as for instance the 

 Oenothera hrevistylis, which in its crosses al- 

 ways behaves as a pure retrogressive variety. 

 Instead of giving an exhaustive survey of 

 hybrids, I simply cite my crosses between 

 Lamarckiana and biennis, as having nearly the 

 aspect of the last named species, and remaining 

 true to this in the second generation without 

 any sign of reversion or of splitting. I have 

 crossed another elementary species, the Oeno- 

 thera hirtella with some of my new and with 

 some older Linnean species, and got several 

 constant hybrid races. Among these the off- 

 spring of a cross between muricata and hirtella 

 is still in cultivation. The cross was made in 

 the summer of 1897 and last year (1903) I grew 

 the fourth generation of the hybrids. These 

 had the characters of the muricata in their nar- 

 row leaves, but the elongated spikes and rela- 

 tively large flowers of the hirtella-ipRYeni, and 

 remained true to this type, showing only slight 

 fluctuations and never reverting or segregating 



