ules and pollen grains
of the same individual must be taken into account in future work there is
evidence from quite a different source. The double stock is an old
horticultural favourite, and for centuries it has been known that of itself
it sets no seed, but must be raised from special strains of the single
variety. "You must understand withall," wrote John Parkinson of his
gilloflowers,[9] "that those plants that beare double flowers, doe beare no
seed at all ... but the onely way to have double flowers any yeare is to
save the seedes of those plants of this kinde that beare single flowers,
for from that seede will rise some that will beare single, and some double
flowers." With regard to the nature of these double-throwing strains of
singles, Miss Saunders has recently brought out some interesting facts. She
crossed the double-throwing singles with pure singles belonging to strains
in which doubles never occur. The cross was made both ways, and in both
cases all the F_1 plants were single. A distinction, however, appeared when
a further generation was raised from the F_1 plants. All the F_1 plants
from the pollen of the double-throwing single behaved like double-throwing
singles, but of the F_1 plants from the ovules of the double throwers some
behaved as double throwers, and some as pure singles. We are led to infer,
therefore, that the ovules and pollen grains {123} of the double throwers,
though both produced by the same plant, differ in their relation to the
factor (or factors) for doubleness. Doubleness is apparently carried by all
the pollen grains of such plants, but only by some of the ovules. Though
the nature of doubleness in stocks is not yet clearly understood, the facts
discovered by Miss Saunders suggest strongly that the ovules and pollen
grains of the same plant may differ in their transmitting properties,
probably owing to some process of segregation in the growing plant which
leads to an unequal distribution of some or other factors to the cells
which give rise to the ovules as compared with those from which {124} the
pollen grains eventually spring. Whether this may turn out to be the true
account or not, the possibility must not be overlooked in future work.

Single
|
+-------------+
Single Double
/ \
Pollen of x Ovule Pollen x Ovule of
pure single | | p