NATURAL HYBRIDS. 159 
NATURAL HYBRIDS. 
By R. Irwin Jiyncu, M.A., V.M.H., Curator of the Botanic 
Garden, Cambridge. 
Frew realise how frequently hybrids occur in nature or the extent to 
which they have been recognised by the systematic botanist. His interest 
in them is not usually that of the readily convinced hybridist ; they force 
themselves upon his attention, and, unwillingly it may be, he is a witness 
to the reality of their existence. To the student of evolution they must 
always be of interest, but I think they must also be of importance to the 
plant-breeder and hybridist, because they belong to the subject of his 
investigation, and having taken an actual place in nature may be expected 
to afford valuable material for experiment and observation. In many 
cases they are actual “ species,’ and none, indeed, know how many so-called 
pure species may not have originated wholly, or in part, by hybridisation. 
In parenthesis, and apart from the present subject, the speculation may be 
advanced that casual hybrids have sometimes a rvéle in nature, as well as 
the permanent entity entitled species. Kerner was a strong believer in 
the origin or making of new species by hybridisation, and he estimated 
that the number of hybrids brought to light within forty years and 
recognised in the Flora of Europe could not be less than a thousand. 
All those certainly could not rank as species, but the time has passed 
when it could be doubted that hybridisation plays a very important part 
in evolution. My point is that the plant-breeder’s work is nothing but an 
intellectually guided form of evolution, which must proceed under some 
of the laws that are concerned in the evolution of Nature. Nature 
attains its ends, it appears, by a circuitous route and through much waste, 
insomuch that few only of a large number of hybrids are permanently re- 
produced, while the plant-breeder, by understanding law, is learning how 
to work directly towards the results he desires, and he is limited only by 
the potentiality of the material at his command. In the study of law very 
much has to be done, and it is with the hope of assisting the ex- 
perimentalist and the observer that I have prepared the following lists. 
They are by no means complete, but they include the majority of the 
genera which are likely to be useful ; andas to the crossing of species, it is 
usual that hybridising habit is similar throughout a genus, though to this 
there are exceptions. All who study hybrids extensively will, no doubt, 
consult “ Pflanzen-Mischlinge,”’ by Focke, but this work was published in 
1881 and is not available to all readers of this report, so that the following 
lists may be of service. 
I have made a selection of British and Continental hybrids, because 
they are most within reach, and being usually hardy are suitable for 
experimental work, while to have found a limitation with wider scope 
would have been difficult. Reference I have given to a single work only, 
