Pollen Mother -cells of Lilium canadense . 231 
the individual resulting from a particular cross will display throughout life 
the same combination of congenital qualities ; and also that different 
individuals resulting from the same cross will closely resemble each other. 
These expectations also are in general realized by the facts presented by 
hybridization experiments. It appears, however, not unnaturally, that the 
balance which may be struck between the more or less conflicting idio- 
plasms is a matter of delicate adjustment, subject to modification by various 
influences, such as differences of nutrition, and perhaps in many cases by 
internal causes which cannot at present be traced. 
As to the general constancy during ontogeny of the characters of 
a hybrid individual, it is a recognized rule that, for instance, the colour, 
shape, and size of the flowers of a hybrid plant are as constant as in 
a pure-bred individual. In the case of the Drosera hybrid already 
mentioned, the characteristic leaf-form prevails throughout ontogeny. The 
same is true regarding the various characters studied by Mendel in his 
Pisum hybrids. 
But it is not difficult to find exceptions to this rule, which illustrates 
the comparative instability of the balance between the parental idioplasms. 
One class of exceptions includes the c mosaic * hybrids, several of which were 
described by Darwin (’68). Among these are Lecoq’s crosses between 
different coloured varieties of Mirabilis , some of which produced flowers 
half of one colour, half of another ; and the case of a mongrel dog, part of 
whose skin was hairy and part naked, the parts being distinctly separated. 
The flowers of crosses between the carnations Scott and McGowan (Swingle 
and Webber, ’98) show, side by side, the colours of the two parents. A 
frequently cited instance is Cytisus Adami , occasional branches or single 
flowers of which revert to the type of either parent. De Vries (’03), who 
considers this plant a true hybrid, and Lotsy (’04) suggest that the reversion 
of certain members may be due to a qualitatively unequal nuclear division 
interpolated among the normal somatic divisions, so that certain cells 
receive only one parental idioplasm in nearly or quite pure form. Correns 
(’03$) and Halsted (’04) have obtained hybrid maize-grains whose endo- 
sperm displays in different parts of the same grain the distinctive characters 
of the two parents. 
A very different class of exceptions to the same rule consists of those 
hybrids which undergo changes during ontogeny. In this class Darwin 
(’68) cites Gartner’s hybrids between Tropaeolum minus and T. majus , 
whose flowers were at first intermediate, but some of which later in the 
season produced flowers in all respects like those of one parent. Cannon 
(’03 a) mentions several analogous cases. Whether such exceptional 
behaviour is due to environmental influences, or to local internal conditions, 
it accords well with the conception of the presence throughout the life of 
the hybrid of two separate, independent idioplasms. 
