594 Species According to the Theory of Mutation. 



to an enlargement of genera. On the other hand it would 

 put a check on the splitting up of genera which has been 

 so much in vogue of recent years, and not less to the 

 elevation of subgenera to the rank of genera. In practice, 

 however, the application of Herbert's suggestion has 

 proved impossible. At that time there were only a few 

 generic hybrids, but their number has undergone a con- 

 siderable increase ; partly no doubt through the arbitrary 

 splitting up of genera mentioned above, but partly also 

 through the rapid accumulation of experimental data. 

 Berhcris and Mahonia (e. g. B. Nenherti) could well be 

 united into one genus. The suggested union of rye and 

 wlieat, a hybrid between which has been raised by Rim- 

 PAu,-^ into a single genus Fnnncntum, is not likely to 

 win much favor; and the fact that Burbank, in Cali- 

 fornia, has raised a hvbrid ho-iw^tn Nicotiana d.nd Petunia 

 which he calls Nicotunia^ will hardly be regarded as a 

 sufficient ground for a systematic union of these two 

 genera. There are now about 150 bi-generic hybrids 

 amongst the Orchids, especially between the genera Lae- 

 Ha, Cattleya, Epidcndruni and Sophronitis, as also be- 

 tween Zygopctahim, Colax and Batemannia.^ 



The practical difficulties which stand in the way of 

 Herbert's proposal are, on the one hand, the fact that 

 the limits to possible hybrid combinations are by no means 

 definite, and on the other hand, the objection, which has 

 so often been raised, that crosses are exceptional phe- 

 nomena and that it would therefore be impossible to 



^ W. RiMPAU, Kreusungslirodnktc Jandzvirthschaftlichcr Cnlfur- 

 pfianzen. Landwirthsch. Jahrb., 1891, p. 20, and PI. VI, Fig. 58. 



^Luther Burbank, New Creations in Fruits and Flowers (Bur- 

 l)ank\s Experiment Grounds, Santa Rosa, California), 1893, with a 

 figure of the Nicotunia. 



' C. C. Hurst, Jotirn. Roy. Hort. Soc., Vol. XXTV, pp. 102, 125. 



