664
D e s c e n d e n z und H y b r i d e n .
1. The mean number of floral organs of any one kind,
and the mean total of floral organ per flower, differ from race
to race.
2. The variability of each series of floral organs, or of the
sum of floral organs, differs from race to race.
3. There is considerable positive correlation between all
the series of floral organs, so far as variation in number goes.
4. The mean number of organs of any series diminishes
as a rule from the commencement of the flowering season to
its close; the rate at which this decrease occurs differs in diffe­
rent races.
5. Certain abnormalities (staminodal petals and lobed petals)
are more frequent towards the close of the flowering season.
K. P e a r s o n .
L., E x p e r i m e n t s
in H y b r i d i s a t i o n , w i t h
s p e c i a l r e f e r e n c e t o t h e E f f e c t of C o n d i t i o n s o n
Dominance.
(Phil. Trans. Roy. Soc. Vol. CXCVI. B.
p. 119—173. 1903.)
This paper records a large series of experiments, in which
various species of Echinids were cross-fertilised, the object being
to discover the effect of varying conditions, either before or
after fertilisation, on the dominance of the characters of one
parent over those of the other. The word „dominance" is
used to denote prepotency with regard to a single character,
or group of characters, as manifested in the hybrid; since the
hybrids were only reared to the condition of a pluteus larva,
it was impossible to discover whether dominance in the Mendelian sense occurred, or not.
The greater number of hybrids were between
Sphaerechinus granular is Q and Strongylocentrolus
lividus cf, and
the characters studied where those of the larval skeleton.
1. The hybrids obtained varied in character, according to the
season at which the experiments were made, and a body of
evidence is given which goes to show that temperature during
development is a chief factor in determining the seasonal diffe­
rence. Since temperature acting on the ova and spermatozoa
before or during fertilisation gave no certain effect, while two
batches of eggs, from the same parents, fertilised together but
reared at different temperatures gave different average results,
the conclusion is drawn that change of temperature does not
affect the dominant or recessive character of the gamete, although
it may affect the degree to which the dominant character is
manifested in the Zygote. 2. The relative freshness or staleness
of the ova and spermatozoa used is stated not to affect
the dominance.
3. The degree of dominance, in any of
the characters observed, was found to vary considerably from
individual to individual, and not to be an absolutely constant
property of all individuals of one species. 4. The behaviour
of the hybrids showed that in spite of the average similarity
DONCASTER,