119 REPORT OF THE CONFERENCE ON GENETICS. 
Rassen- und Gesellschafts-Biologie, I., p. 187, 1904. See also Plate’s article 
“Die Mutationstheorie im Lichte zoologischer Tatsachen.’’ (Comptes rendus 
du 6me Congrés intern. de Zoologie, 1904-1905.) 
19. MacDoveat (anp VatL, SHULL, AND SMALL).—Mutants and Hybrids of 
the Cinotheras (Papers of Station for Experimental Evolution at Cold Spring 
Harbour, New York, Nr. 2 Washington, 1905), emphasises and exemplifies 
the necessity of analysing the species before entering on the question of mutation. 
This is quite in accordance with my own views. 
20. Lana.—Ueber die Mendel’schen Gesetze, Art- und Varietitenbildung, 
Mutation und Variation, insbesondere bei unseren Hain- und Gartenschnecken. 
(“ Verhandl. d. Schweiz. Naturforschenden Gesellschaft, Luzern, 1905,” 1906.) 
21. Vitmorin.—Notices sur l’amélioration des plantes par le semis. 
(Nouvelle édition, Paris, 1886.) Contains Louis Vilmorin’s highly interesting 
papers on heredity from the time before Darwin. 
22. GaLTon.—Natural Inheritance. (London, 1889.) 
DISCUSSION. 
The President: Professor Johannsen has been dealing with a problem 
of extreme difficulty. He analyses types according to their quantitative 
relations, and he shows that what we call one type is in reality a great 
number of types which are each true to a certain definite average 
weight. His experiments go to indicate that these averages are in 
themselves pure factors. What happens when these pure types differen- 
tiated by small fluctuations are crossed, we do not know, but there is a 
suggestion that segregation occurs. 
Professor Plate, of Berlin: If you take a pure type which is always 
self-fertilised, you cannot expect variation; but as soon as you change the 
outward conditions of the pure type—I do not say that the variations 
would not be small, but on the one side or the other there will be 
continuous variation. If the continued conditions are fixed, there would 
not be any change, either to the one side or the other, and that would be 
what Darwin calls “ continuous variation.” Therefore Professor Johann- 
sen has not convinced me that continuous variation does not exist. If 
we look into nature we can always get continuous variation. For instance, 
I have studied snails which are to be found in the Bahama Islands, and 
although there were the greatest variations they were continuous. 
Mr. G. U. Yule, University College, London : Iam afraid I haye not 
yet been won entirely to Professor Johannsen’s views. It is quite true 
that he has not been able to observe any differentiation, even though he 
has selected the weight or width of his beans throughout five generations ; 
but, as I suggested in a short review of Professor Johannsen’s work, it 
would be quite possible that that should happen if the variations due 
to environment were large compared with the variations in the germinal 
types, and | think it will be found that the somatic variation in these 
beans is very large indeed compared with the germinal variation. If, 
under such circumstances, you select according to somatic character, 
there will be only a very slight selection of germinal types, and this may 
well be masked by somatic fluctuations. I judge, from other things we 
know, that the germinal variation cannot be absolutely zero. To justify this 
statement I fear I must mention a quantity which I shall have to mention 
again later on, and that is the correlation-coefficient of the biometrical 
