Darwin’s Cross and Self-Fertilization of
plants.*
DY PROF. w. 3' BEAL
Foreign-Crossed Stock Ahead.
In the case of Mimulus luteus (monkey flower),
a small herbaceous ornamental plant, Mr. Dar¬
win found for three successive generations that
the crossed plants exceeded in height those which
were self-fertilized, but in the fourth generation
one of the self-fertilized plants beat its crossed
opponent. “ This victorious self-fertilized plant
consisted of a new white-flowered variety, which
grew taller than the old yellowish varieties.
From the first it seemed to be rather more fer¬
tile, when self-fertilized, than the old varieties
and in the succeeding self-fertilized generations'
became more and more self-fertile. In the sixth
generation the self-fertilized plants of this vari¬
ety, compared with the crossed plants, produced
capsules in the proportion of 147 to 100, both
lots being allowed to fertilize themselves spon¬
taneously.” This instance appears analagous to
the vigorous self-fertilized morning-glory which
appeared on the sixth generat

appeared on the sixth generation. In the eighth
self-fertilized generation some flowers of Mimulus
were self-fertilized; other flowers were crossed
with those from distinct plants of the same lot,
and “ others were crossed with a new stock of
plants from Chelsea. The Chelsea crossed seed¬
lings were to the intercrossed in height as 100 to
56, and in fertility as 100 to 4 ; and they were to
the self-fertilized plants in height as 100 to 52,
and in fertility as 100 to 3. These Chelsea-
crossed were also much more hardy than the
plants of the other two lots.” This remarkable
result brings out with great force the idea itali¬
cised in my previous article*, that crossing a vari¬
ety or species with a foreign stock, often pro¬
duces Results Wonderfully Favorable.
This is the great leading point conclusively
proved by experiments cited all through the book.
It towers above all others in such a way that it
cannot be easily overlooked. There is need of
many other experiments in the same direction in
different portions of our country, and especially
are experiments needed in crossing with for¬
eign stock all of our garden vegetables which
store up nourishment in roots, as beets, turnips,
salsify, carrots, parsnips, radishes and the like.
Here is a new field not yet worked, and one well
worth a good trial. In case of trees and shrubs

worth a good trial. In case of trees and shrubs
and other plants too, it is an easy matter to have
pollen sent by mail from a distance. The writer
is trying this with apples and grapes.
In case of the Mimulus above mentioned the
third generation of self-fertilized plants were
allowed to fertilize themselves spontaneously'
Another lot were grown beside them from crossed
seeds. “The crossed plants produced a large
number of capsules, whilst the self-fertilized pro¬
duced very few and poor ones.” The seeds in
the crossed-capsules excelled those self-fertilized
as 100 exceeds 34. Experiments were made
with these two lots of seeds showing “ in a decis¬
ive manner the superiority in constitutions,
vigor of the crossed over the self-fertilized plants.
The flowers of self-fertilized plants in the exper¬
iments made became more uniform than those
which were crossed. This was quite mars
with Mimulus, Ipomcea and Diantin'S. Mr ent
low raises the query, why is this when wild don¬
ers are so uniform ? These are certainly man
times abundantly crossed and often appear mII
alike even when growing in different localities
quite remote from each other on a great variety
of soils. Obstacles Show Quality.
In comparing the crossed with the

Obstacles Show Quality.
In comparing the crossed with the self-ferti;
ized plants Mr. Darwin usually placed one,,
each at the same time on different sides of t
same pot. Mr. Henslow objects on the ground
if not crowded, the self-fertilized plants wou
be relatively better. In some cases, also, 17
Darwin places two lots of plants in crow

*For the first article on this subject see “Darwin's New
Book ” June Scientific Farmer.


131
masses in the same pot or box. In the third
generation of Petunia Violacea “ both lots grew
extremely crowded; the crossed were twice as
tall as the self-fertilized.” Other examples of
a similar nature are given in the book. Mr.
Darwin, in Volume II of his Animals and Plants
under Domestication says, “ It is important that
the two lots struggle with each other, for if sown
with plenty of room and good soil, there is often
but little difference in their growth." In other
words the self-fertilized are more easily overcome
by surrounding obstacles. Like pampered ani¬
mals, they cannot endure great hardships. In
cultivating plants on the farm and garden in
many cases they are grown so close as to crowd
each other. If so, seeds of crossed plants are
generally the best, and most profitable to sow.
Effect of Locality.
Another fact mentioned in the case of Escho-
scholtzia is not a lone instance. In South Amer¬
ica the self-fertilized flowers are sterile, while if
seeds are sown in England the self-fertilized
plants are the most productive and do the best.
All these things show the great need of many
more experiments, and the danger of drawing
conclusions too hastily from limited experience.
As Darwin says, “ The fertility of a plant is a
most variable element, depending on its age,
health, nature of the soil, amount of water given
and temperature to which it is exposed.” To
some extent we are groping in the dark. We do
not know all the conditions about any one exper¬
iment.

Mr. Henslow brings up another point which
should demand the careful attention of men of
science. Many of our worst weeds are self-
fertile. In a large majority of cases weeds are
foreign invaders — natives of other countries,
but this is not the case with all weeds. In some
cases, the superior vigor of foreign weeds may
be, and doubtless is to some extent due to a
change of location. Why do our weeds thrive
so well? The tallest cabbage plants are not
always the best. In his experiments Mr. Dar¬
win cut down and weighed the fully-grown plants.
Six self-fertilized plants of the third generation
when they had formed heads weighed 142.25
ounces; six plants from pollen of fresh stock
weighed 619 ounces. That is, the six “ crossed
plants averaged 108.16 ounces, whilst the six
finest self-fertilized plants averaged only 23.7
ounces, or as 100 to 22.” Here again, we see an
“ enormous benefit ” in favor of crossing a variety
with foreign stock of the same variety, which had
grown for a few years under different conditions.

Differing Results.
The scarlet runner bean (Phaseolus multifloras'),
in one case when covered up yielded about one-
third and in another case about one-eighth “ of
the number of pods which the same number of
uncovered plants growing close along side pro¬
duced. This lessened fertility was not caused
by any injury from the wet,” as some of the pro¬
tected flowers were artificially fertilized and pro¬
duced well. Dr. Ogle had tried a similar exper¬
iment with a total failure of fruit when the
flowers were protected. Phaseolus vulgaris, a
closely related species, proved highly fertile
when insects were excluded. In England the


varieties of the sweet-pea rarely or never cross
when grown near each other. This may not be
true in other places, as in Italy “ it is the fixed
opinion of gardeners there that the varieties do
intercross,” that they cannot be kept pure unless
protected or sown in separate places. Let every
person take warning from such examples and
not draw hasty conclusions from one illustration
or experiment, or the behavior of a single speci-
men. I'1 some place a man does not see any
bees working on a certain kind of plant, when
nib’ straightway he announces that bees do not work
aly" on that species. Perhaps the bees did work at
" other times of days; if not, perhaps they worked
in other seasons or in other locations. Examples
could be found to illustrate the above supposed
cases. Pisum Sativum, the common pea in Eng¬
land was perfectly fertile without the aid of insects
(Concluded next month.)