MENDELIAN CHARACTERS 217 
have some hesitation in accepting them without further 
study. 
It must be admitted that the suggestion that Men- 
delian segregation may be a universal phenomenon 
accompanying the formation of the germ-cells of all 
animals and plants is one which will be disputed by 
many biologists. There is ample evidence, they will 
say, of first crosses breeding true in the case of 
numerous plant and animal hybrids. But there are 
several points to be considered before we can accept 
the mere fact of a uniform progeny as sufficient evidence 
that there was nothing in the nature of segregation 
amongst the gametes of the hybrid. 
To prove a negative is proverbially difficult, and 
the attempt to show that hybrid characters exist 
which do not segregate in the germ cells of the hybrid 
is no exception to this rule. In favour of the opposite 
contention the following considerations may be 
alleged : 
The characters for which non-segregation has been 
asserted are generally complex and difficult to define. 
Such characters, for instance, are the general habit 
of a plant or the general shape of a flower. Characters 
such as these may reasonably be supposed to owe 
their appearance to the interaction of a considerable 
number of independent allelomorphs. 
Where two such factors are concerned, in cases 
where the heterozygote form is intermediate, we 
should expect one out of sixteen F, individuals to 
resemble each parent form, the remaining fourteen 
plants being more or less intermediate. 
