326 LOCK : STUDIES IN PLANT BREEDING 
likely that these factors, to say nothing of possible cases of 
false hybridism and other non-Mendelian phenomena, would 
have some effect upon the values of parental correlation. 
Moreover the value *45 — *5 is arrived at from the average 
of a number of cases which show a very much wider range. 
It seems, therefore, unjustifiable to apply the average result 
of biometric computations as a criterion for testing experi¬ 
mental observations upon the behaviour of the gametic 
representatives of definite characters in definite cases. 
On the other hand, if the applicability of Mendel’s Law 
continues to be extended in future at the same rate as it has 
been during the past few years, it may become necessary to 
examine whether definite reasons cannot be discovered to 
account for the wide deviation in certain cases of the observed 
value of parental correlation from the value *33. 
On the whole, it seems clear that in the law of ancestral 
heredity we have a foreshadowing of the more precise and 
definite law of Mendel. 
III.—THE SHAPE AND COLOUR OF THE SEEDS 
OF PEAS . 
In recent years a considerable number of “exceptions 
to Mendel’s Law” have been cited with respect to these 
characters. One such exception, indeed, was known to 
Mendel himself, namely, the existence of a correlation 
between a coloured testa, coloured flowers, and purple spots 
in the axils of the leaves. In Mendel’s experiments none of 
these characters ever made its appearance, except in associa¬ 
tion with the other two. In such a case as this we may 
suppose with Correns (15) that the different external mani¬ 
festations depend, in part, upon a single internal “Anlage.” 
On the other hand, Tschermak has described races in which 
certain of these characters appear without the others (63). 
Correns himself was the first (11) to note an exceptional 
case, in which the colour of the testa behaves in a different 
manner from that which Mendel described. In his cross 
