278 REPORT OF THE CONFERENCE ON GENETICS. 
THE IMPORTANCE OF HYBRIDISATION IN THE STUDY 
OF DESCENT. 
By Dr. E. Tscuermak, of the Hochschule fir Bodencultur, Vienna. 
Up to a few years ago it was the opinion of scientists that hybridisation 
was of no great consequence in the production of new forms or in the 
study of evolution. Practical breeders, on the other hand, had long 
learnt to regard artificial crossing as a means which in certain cases could 
produce apparently new forms. In any case, no sort of general regularity 
seemed to obtain. So as to secure the commercial benefits of lucky 
accidents, the cloak of secrecy was even thrown by many breeders over the 
origin of their new products. Consequently, even now many forms are 
wrongly described as hybrid; and on the other hand many novelties, the 
origin of which is not given, may be referred with certainty or probability 
to an intentional or an unintentional cross. 
The knowledge that artificial hybrids between species possess very 
sheht fertility, and that their produce may eventually often throw back 
to one or other of the parent forms, had formerly a noticeable effect in 
depreciating the value of hybridisation. It is true that Girtner, Charles 
Darwin, and Focke recognised that apparently new characteristics may 
appear in hybrids, but they exclusively regarded such appearances as 
cases of throwing back to one or other of the parent forms—that is to 
say, aS atavism. 
Besides this historical or phylogenetic aspect, the claim of hybridisa- 
tion to be regarded as having a direct role in the production of new forms 
and combinations has been established. For, according to the Mendelian 
law, which I may to-day regard as generally known—in the production of 
new hybrid forms all possible combinations of the parental characters 
occur.* In these results of segregation some may at first sight strike as 
novelties ; their novelty, however, is due to the combination of characters, 
and not to the intrinsic characters themselves. This limitation appears— 
though only to the inexperienced eye—to be suspended in those interest- 
ing cases in which apparently simple characters of the parents are 
resolved into several component parts, and these components are recom- 
bined according to the Mendelian law. ‘This phenomenon, which Bateson 
describes as “analytical variation of compound characters or allelo- 
morphs,’ is specially noticeable in colour characteristics (de Vries, 
Tschermak, Bateson, Correns, and others). Also the converse case, 1.é. 
the fusion or synthesis of hitherto separate components into an apparently 
new simple character, is possible—constituting a synthetical variation by 
combination of unit cbaracters according to Bateson. 
* That monstrous structures Mendelise both in the botanical and zoological 
kingdoms is amply proved. My own experiments, for instance, show that fasciation 
in Piswm behaves as a typical Mendelian recessive when crossed with the normal 
stem—as also do the compound ears of wheat and barley in crosses with normal * 
ears. 
