Darwin’s Cross and Self-Fertilization of
Plants. II.
BY PROF. W. J. BEAL.
Early Maturity Gained.
I have said that plants crossed with a foreign
stock were in a great majority of cases taller,
larger, heavier, more vigorous, or better able to
endure crowding by other plants. They also
endured inclement weather better. In another
respect Mr. Darwin has shown their superiority.
In 58 cases “the period of flowering of the
crossed and self-fertilized plants was recorded.
In forty-four of them a crossed plant flowered
first either in a majority of the pots or in all; in
nine instances a self-fertilized plant flowered
first, and in five the two lots flowered simultane¬
ously. One of the most striking cases is that of
Cyclamen, in which the crossed plants flowered
some weeks before the self-fertilized in all four
pots during two seasons. ” In some cases, as with
Lupinus luteus and Clarkia elegans, the crossed to
the self-fertilized plants in height were to each
other as 100 to 82, yet Clarkia flowered first.
Numerous experiments showed that the cross¬
ing of one flower with that of another on the
same plant seldom if ever does any good. All
the flowers are subjected to the same conditions.
In tables given, “in thirty-five out of fifty, flowl
ers fertilized by pollen from a distinct plant yield
more, sometimes many more seeds than flowers
fertilized with their own pollen ; and they com¬
monly set a larger proportion of capsules.”
. Considering all the facts brought forward “ it
is difficult to avoid the suspicion that self-fertil¬
ization is in some respects advantageous,” though
he says if this be really the case the advantage
is quite insignificant compared with that from a
cross with a distinct plant, and especially with
one of a fresh stock. In ten out of sixteen cases
the self-fertilized seeds were either superior or
equal to the crossed in weight. This the author
partially accounts for “ by the self-fertilized capsules 

144
containing fewer seeds,” which on this
account had a better chance to receive an abun¬
dant supply of nutriment.
Effect on Germination.
Fig. 5.—Wild Cabbage.
In twenty-one cases a record was kept of the
relative period of germination of crossed and
self-fertilized seeds. In one case the seeds germ-
the self-fer¬
tilized seeds
germinated
before the
crossed, and
in the other
ten the
crossed
seeds ger-
mi n a t e d
first. After
knowing
the great
advan t a g e
to be deriv-
e d from
cross-fertili¬
zation, we
are prepar¬
ed to under¬
stand that
honey is
placed in
flowers a s
wages to
pay insects
for serving
the plants. The gay colors and odors are adver¬
tisements to call the attention of insects to the
rich supplies of food in store for them. Saun¬
ders, of Canada, cut off the petals of raspberries,
and by so doing made it difficult or impossible
for the bees to find honey. “ Almost every fruit
which is devoured by birds presents a strong
contrast in color with the green foliage, in order
that it may be seen and its seeds freely dissem¬
inated.”
Natural Provision for Crossing.
Among many other topics of interest Mr. Dar¬
win gives part of a chapter on the means which
favor or ensure flowers being fertilized with
pollen from a distinct plant. We have seen that
a cross of different flowers on the same plant does
but little good. One insect will often visit an
astonishingly large number of flowers in a small
space of time. They cannot tell whether a flower
contains honey or not till they try it. In this
way any flower is frequently visited by many
insects in turn, some of which will very likely
bring pollen from other plants. A single plant
of a species rarely grows alone. There are others
near by. Dioecious plants* must be crossed.
When moncioust there is a good chance for a
cross, especially where the anthers ripen before
the pistils are ready for the pollen or the reverse.
The expansion of only one or a few flowers at a
time on a plant favors a cross of two distinct
plants. Dimorphous is a term applied to plants
which have stamens and pistils of two different
lengths. For example, the flowers of Primula
on one plant will have all the pistils running to
the top of the tube of the corolla, while the sta¬
mens will be below; yet on another plant the
stamens may be near the top of the tube while
the pistil is below. This is the case with Bou-
vardia, Houstonia and many others. They are
dimorphous. The long styles on one plant are
more certain to be fertilized by the tall stamens,
and when so crossed produce seeds best; while
the short stamens or those low down are fitted to
cross the short styles.
He planted a white kohl-rabi, a purple kohl¬
rabi, a Portsmouth brocoli, a Brussels sprout, and
a sugar-loaf cabbage (varieties of one species)
near together and left them uncovered. A ma¬
jority of seedlings from these seeds in all five
beds were mongrelized in the most complicated
manner. Some other experiments were made
•Having male and female flowers on different plants.
tHaving male and female flowers on same plant, but the
sexual organs not in the same flower, as in Indian corn.

with other plants giving similar results, as onions
and mimulus.

Difference in Pollen.
In numerous cases he placed pollen on the
stigma from anthers of the same plant, and in
twenty-four hours added pollen of another vari¬
ety. In every instance some or all the pistils
bore seeds which showed they were crossed by
the last application of pollen. If one flower is
fertilized with pollen which is more efficient than
that applied to the other flowers on the same
peduncle, the latter often drop off. This was
shown by experiments of Herbert and others.
The amount of pollen produced by plants which
are dependent upon the wind to fertilize them is
very large. Pollen in some cases drifts for hun¬
dreds of miles and rises to the height of 500 to
1,000 feet. This gives a great opportunity for
many of our evergreens and other trees and
plants to be crossed by distant plants.

Bees as Specialists.
Chapter eleven is devoted to the habits of in¬
sects in relation to the fertilization of flowers.
From a previous paper read at the Michigan
Bee-keeper’s Convention the writer of this review
remarked, that “ Individual bees have been ob¬
served to behave differently about flowers, in
some respects, from a majority of bees. Some
are eccentric. They have their peculiarities.
Nageli put artificial flowers to branches, and
used essential oil on some, and on others he used
no oil. The odor attracted them to the flowers
containing it. Aristotle, 2,000 years ago saw
that hive bees worked continuously on flowers of
the same species. They even do so when the
flowers are not all colored alike, as in some plants
in our flower gardens. By this means they econ¬
omize time. They get the hang of it. They
learn how better to make more rapid motions,
and to make every motion count. The same as
is true of people who become expert in certain
parts of any trade after much practice in often
repeating the same operation.”

A Practical Suggestion.
The twelfth and last chapter of this fertile
book is devoted to general results. Like most of
the other chapters, to do it justice would require
long quotations. The seeds from a plant are
benefited by the flowers having been fertilized by
pollen of another plant which had been subjected
to quite different conditions. This is brought
about in many instances in the same spot where
seeds have lain covered or dormant for some years,
and then are turned up or placed in favorable
condition to grow and mix with plants from seed
produced in later years. Seeds are no doubt
influenced by being kept for a long time. “ Those
which were matured during different seasons,
will have been subjected during the whole course
of their development to different degrees of heat
and mois¬
ture.” “ It
is a common
practice
with horti¬
culturists to
obtain seeds
from an¬
other place
having a
very differ¬
ent soil, so
as to avoid
r a i s i n g
plants for a
long succes¬
sion of gene-'
rations un¬
der the same
Fig. 6.—Kale. c o nditions ;
but with all the species which freely intercross
by the aid of insects or the wind, it would be an
incomparably better plan to obtain seeds of the
required variety, which had been raised for some
generations under as different conditions as pos¬
sible, and sow them in alternate rows with seeds
matured in the old garden. The two stocks would
then intercross, with a thorough blending of their
whole organizations, and with no less of purity
to the variety; and this would yield far more
favorable results than a mere exchange of seeds.”
Agricultural College, Lansing, Mich, Aug., 1877.

[Those interested in this very interesting re¬
view, may be interested to learn that the book is
for sale at this office. See advertisement.—Eos.]