210 REPORT OF THE CONFERENCE ON GENETICS. 
THE HEREDITARY TRANSMISSION OF COLOUR IN 
CROSS-BREEDING. 
By C. L. W. Noorpuun (Groningen). 
In the August number (1904) of “ Album der Natuur,”’ in which I gave a 
short explanation of Mendel’s law of heredity, I ventured the opinion that 
experiments such as Mendel described, if prosecuted for a course of years, 
would lead to other results, because the dominance of the wild type 
over a variety is dependent upon the length of time during which that 
variety has been bred pure. 
As is well known, the Abbot Gregor Mendel made the discovery that 
in crossing plants of the original wild type with any of its varieties, it 
mattered not which, all the resulting cross-breds had the external charac- 
teristics of the original type. The discovery and the behaviour of subse- 
quent generations of these cross-breds induced him to relate the results of 
his experiments to the Society of Natural Science in Brinn, in February 
and March 1865, with the result that it was subsequently known as 
Mendel’s law of heredity. Mendel selected from several seed shops some 
thirty-four different varieties of peas, and subjected them to a two years’ 
test in order to make sure that they bred true. 
It was some years before Mendel’s law attracted general attention. 
In fact, it was not until the opening of the present century that anyone 
took up Mendel’s ideas, and the discovery was made that an extensive 
field of investigation had been opened to the student of natural science. 
The result of my personal experiments is that I am not altogether able to 
agree with the conclusions which have been deduced. 
We are aware that corresponding varieties of animals and plants 
may by careful selection—that is, by the rigid weeding out of those 
individuals showing a tendency to vary—after a few generations be 
induced to breed true, and to show no tendency to revert to the original 
type. In proportion to the period of time during which varieties have 
been bred true will their power to hereditarily transmit their charac- 
teristics be increased, and the force of reversion to the original wild type 
be diminished ; whilst, on the other hand, a variety which is comparatively 
new will display this tendency to revert in a very much more accentuated 
degree. Hence it follows that if a comparatively modern variety is 
crossed with the original wild type, the latter shows itself as dominant or 
preponderant in its influence on the offspring ; whilst if a variety which 
has been bred pure for a great number of years is similarly crossed, its 
characteristics have sufficient weight to dominate those of the wild type, _ 
and reversion is of rare occurrence. In view of what I have above stated, 
I have come to the conclusion that what is called Mendel’s law is no law 
at all. The experiments I have made during the present year have 
satisfied me that hybrids sprung from a cross between the original wild 
type and a long-established variety of it show the characteristics of the 
