128 REPORT OF THE CONFERENCE ON GENETICS. 
place in such cases. In pure breeding, segregation of the pair of factors 
for ‘ presence’ would be normal, and in the case of two ‘absences ’ neither 
pairing nor segregation would be necessary ; the only difficulty, therefore, 
is as to how segregation takes place in the gamete of a hybrid carrying 
some non-paired factors. 
Such a process, however, is not inconceivable, for in most cases there 
would be both paired and unpaired factors together, and where segregation 
of the paired factors takes place it is conceivable that the same process 
might also segregate the unpaired factors, the ‘presence ’ factor going into 
one gamete, nothing corresponding with it going into the other. 
All three vlews are possible, and all are open to some objection ; in 
the present state of knowledge it is difficult to say which of the three is 
the most reasonable. On the whole, the last view, that ‘absence’ is simply 
nothing, certainly appeals to the practical mind, and is perhaps, of the 
three, the one least open to objection. 
On this view mutational variations may consist simply of the addition 
of new unit-characters and the subtraction of old ones. 
The evolution of races, of plants under cultivation and animals under 
domestication, has most certainly been made possible by these mutational 
variations. 
The precise determination of the unit-characters in plants and 
animals—by Mendelian analysis or otherwise—is therefore of the utmost 
importance both to the biologist and the practical breeder. 
The biological problem of the future will be not so much the origin 
of species as the origin of unit-characters. 
DISCUSSION. 
Miss Wheldale, Cambridge, referring to Mr. Hurst’s ‘white’ 
Antirrhinums, said there were true albino Antirrhinums existing, but 
those shown by Mr. Hurst were cream, a colour which contained some 
yellow. Some creams by self-fertilisation would produce creams, yellows, 
and whites. 
Sir Michael Foster: It would be much more valuable if we called 
things according to their spectrum nomenclature. We should not then 
have any confusion. 
The President asked if any work giving the spectrum names of colours 
were published which ordinary people could understand. 
Professor Plate said there was such a publication called Jordan, 
Farbentafellen, to be obtained from Jiisfel & Géttel, booksellers, Leipzig. 
The ‘“ Répertoire de Couleurs,’ published under the auspices of the 
French Chrysanthemum Society, a copy of which was procured from the 
Society’s Library, was here produced and handed round the Conference. 
Sir Michael Foster: Sir Philip Magnus has shown that there is no 
difficulty in the matter, and everyone has seen the rainbow. 
The President remarked that the difficulty was not in the nomen: 
clature. It was a question of how many factors went to make up these 
colours. 
Professor Wittmack, of Berlin; We have heard that in this white there 
is yellow. It might be possible to ascertain what we want to know by 
