Pollen Mother-cells of Li limn canadense . 229 
not intermediate, but quite different from that of either parent. This 
occurs frequently with reference to qualities which may be taken as 
indicating an increased or decreased vigour in the offspring ; as, for instance, 
Burbank’s walnut hybrid (Swingle and Webber, ’98), a cross between 
Juglans 7'egia and J. Californica , which grows twice as fast as the 
combined growth of both parents. In the same category is a result 
obtained by Mendel (’65), who found that crossing a long-stemmed and 
a short-stemmed variety of pea gave a hybrid with a stem longer than that 
of either parent. The flower colours of several of Correns’ (’02) Mirabilis 
hybrids are analogous phenomena ; for instance, crosses between a white- 
flowered (M. Jalapa alba ) and a yellow-flowered race ( M . Jalapa flava) 
have red flowers. In the appearance of a hybrid character entirely different 
from the corresponding character of either parent, there is, as Bateson (’02) 
suggests, something analogous to the result of a chemical reaction. Since 
the idioplasm is composed of a complex chemical substance, or, more 
properly, substances, and since, as I have pointed out, the possibility of 
some interaction between two parental idioplasms within the same nucleus 
is not excluded by anything that we know at present, and since, further, 
the determination of cell characters by the idioplasm undoubtedly involves 
a series of chemical reactions, it is not surprising that we should obtain 
results of this character in many instances of the combined action of two 
different idioplasms. 
In discussing such cases as those last mentioned it is necessary to be 
certain that, with respect to the quality in question, both parents were 
pure-bred ; otherwise, the appearance of a character different from the 
corresponding character of either parent may be simply the reappearance 
of a quality of a more remote ancestor, and not at all the result of 
a combination of the two parental qualities. Cases of the appearance of 
a character different from that of either parent are, therefore, unless the 
pedigree of the parents is fully known, liable to the suspicion that they are 
merely due to the reappearance of a latent or recessive allelomorph. 
On the other hand, a conflicting action of the parental idioplasms may 
result in a quality which is in no sense intermediate, but which exactly 
resembles the corresponding character in one parent. It was the observa- 
tion of such phenomena that led Mendel (’65) to the conception of parental 
qualities as either ‘ dominant ’ or ‘ recessive.’ When, for instance, he 
crossed two varieties of Pisum> one having green, the other yellow, 
cotyledons, all the offspring had yellow cotyledons ; in other words, the 
character of possessing yellow cotyledons is dominant, that of possessing 
green cotyledons is recessive. In the same way, the possession of round, 
smooth seeds is a dominant quality, that of angular, wrinkled seeds is 
recessive. The so-called ‘law of dominance’ was never stated by Mendel 
as a general law ; and cases of intermediate character similar to those 
