150 REPORT OF THE CONFERENCE ON GENETICS. 
A CONTRIBUTION TO THE STUDY OF SPONTANEOUS 
HYBRIDS IN THE EUROPEAN FLORA. 
By Monsteur E. G. Camus. 
GENERAL OBSERVATIONS. 
Ir is only exceptionally that the older writers on systematic botany 
refer to hybrid plants. Hybridisation was regarded in their days as an 
exceptional event, and consequently of little importance. To-day it is 
admitted that hybrids are much less rare than had been supposed. In 
certain species (Nasturtiwm, Viola, Cistus, Dianthus, Epilobvum, Rubus, 
Rosa, Potentilla, Cirsiwm, Carduus, Centaurea, Hieracium, Verbascum, 
Mentha, Rumex, Potamogeton, Salix, Orchis, Ophrys, Serapias, Carex, 
&c.) hybridisation is so ordinary an event that it becomes almost common- 
place. One must recognise that it is necessary to study the forms tainted 
by irregular crossing and distinguish them from the species to which they 
belong, so as to fix the limits of the variation of such species. Terato- 
logical forms must further be eliminated, and then the species remain 
true within the limits of variation. 
The botanists of to-day are therefore right in their works (other than 
in quite elementary ones) in according to the study of hybridisation the 
place which it should occupy. 
I would ask permission to lay before you the general results of the 
researches and observations which have been devoted to this subject. Much 
is due to others, but the limits of this communication will not allow of 
my going into the historical side of the subject. My own observations on 
hybrids have extended over more than thirty years of herborisation. 
Devoted collaborators have aided me by their counsel and by the com- 
munication of most important documents. The curators of the large 
Parisian herbaria have also been of great assistance. I therefore hope 
that the observations of which I submit a réswmé will prove of some 
value. 
The study of spontaneous hybridisation shows that very considerable 
differences exist in the families and even in the genera which have been 
under observation. 
Gaertner with reason has said that there are no general laws on the 
subject of fertility or sterility in hybrids. 
The experiments of Naudin have shown that of done different hybrids 
about thirty have produced seeds which germinated. 
There is a distinct relation between the fertility and the proportion of 
pollen-grains which are normally formed. 
Hybrids have a tendency to revert to specific forms by the operation 
of their own pollen, and also in forming quadroons as the result of a 
second crossing with one or other of their parents, which may thus be 
shown :— 
(Ax 3B) x {A x B); (A xaB)cea and (A x B) xB 
