IMPORTANCE OF HYBRIDISATION IN THE STUDY OF DESCENT. 283 
I think that the little which I am able to contribute suffices to show 
that hybridisation is of no inconsiderable importance for the precise study 
of descent, since new forms may arise by crossing—just as they may by 
adaptation, by discontinuous variation or mutation, and—as was formerly 
held—by selection of continuous variations. Hybridisation thus presents 
us with a rich source of forms, and constitutes not rarely a method of 
experimentally testing questions of ancestry.* 
DISCUSSION. 
The President: Iam sure we heartily welcome Professor ‘I'schermak 
amongst us as one who took a part in the original discovery of this 
principle. He had many difficulties to contend with, difficulties which 
would have quenched a less ardent zeal than his. I have had the pleasure 
of seeing the garden in Vienna where he works, and anyone who has seen 
the work carried on under such conditions must realise the immense 
advantage it would be to those engaged in such work to have a properly 
equipped and adequately appointed garden with all the necessary labour 
and technical skill at command. It is to be hoped that in this country 
there will before long arise such institutions, in which this work can be 
carried on, and I feel that such a Conference as this may do something to 
stimulate public interest in such matters and lead to the endowment of 
such institutions. 
Turning to the paper itself it deals with a great variety of topics 
which it is impossible to speak on now. It raises the interesting question 
as to the production of new forms in crossing. Dr. Tschermak’s work 
has shown that the appearance of such new forms is in reality due to 
recombinations of characters which are frequently introduced, though 
perhaps one does not always perceive them. He speaks of the difficulty, 
that has been noticed by others, of knowing whether the older or the 
more recent character will be dominant. His researches show that 
there is no general rule on that point. You cannot say, and nothing 
but actual experiment will show, whether the older or the more recent 
character will dominate. Then there are questions of difficulty from the 
fact that the forms which appear through crossing may be continuously 
connected, and that fact Dr. Tschermak attributes to the multitude of 
characters that have come in, and the vast complications that may be 
introduced through their many combinations and inter-connections. ‘To 
the same fact he, I think, attributes the mixed F,. That may be due 
to the fact that, though parental forms may appear to be alike and 
true to type, yet they may contain a number of cryptomeres, or hidden 
characters, whose influence does not appear as characters until they 
meet a complementary character. The appearance of these novelties in 
later generations he speaks of as hybrid mutations. He might have 
gone on to say that the appearance of such hybrid mutations raises the 
important question as to the extent to which the mutations of de Vries 
are due to similar occurrences. 
* Cp. my paper “Die Lehre von den formbildenden Faktoren,” J./. f. Pflanzen- 
und Thierziichtung, 1903 ; “Ub. Bildung neuer Formen durch Kreuzung,” Verl. d. 
internat. Bot. Kongress. in Wien, 1905. 
