Front Range Seed Analysts
1998 Seed Forum Volume 12 Number 4
Charles Darwin, Seed Analyst
ed. Annette Miller
Excerpts from The Origin of Species
We all know Charles Darwin as the famous nineteenth century naturalist who proposed that new species arise by means of natural selection. In addition to being a world traveller, a pigeon breeder, barnacle taxonomist, and earthworm researcher, he was also a seed analyst! His book The Origin of Species has a fascinating section about testing seeds for germination after immersion in salt water. Darwin was trying to figure out how islands end up with the array of species found on them. The following excerpts are from Chapter 12.
"…In botanical works, this or that plant is often stated to be ill adapted for wide dissemination; but the greater or less facilities for transport across the sea may be said to be almost wholly unknown. Until I tried, with Mr. Berkeley’s aid, a few experiments, it was not even known how far seeds could resist the injurious action of sea-water. To my surprise I found that out of 87 kinds, 64 germinated after an immersion of 28 days. It deserves notice that certain orders were far more injured than others: nine Leguminosae were tried, and with one exception, they resisted salt water badly; seven species of the allied orders, Hydrophyllaceae and Polemoniaceae, were all killed by a month’s immersion. For convenience’ sake I chiefly tried small seeds without the capsule or fruit; and as all of these sank in a few days they could not have been floated across wide spaces of the sea, whether or not they were injured by the salt-water. Afterwards, I tried some larger fruits, capsules &c., and some of these floated for a long time. It is well known what a difference there is in the buoyancy of green and seasoned timber; and it occurred to me that floods would often wash into the sea dried plants or branches with seed-capsules or fruit attached to them. Hence I was led to dry the stems and branches of 94 plants with ripe fruit, and to place them on sea-water. The majority sank rapidly, but some which, whilst green, floated for a short time, when dried floated much longer; for instance, ripe hazel-nuts sank immediately, but when dried, they floated for 90 days, and afterwards when planted germinated; an asparagus-plant with ripe berries floated for 23 days, when dried it floated for 85 days, and the seeds afterwards germinated; the ripe seeds of Helosciadium sank in two days, when dried they floated for above 90 days, and afterwards germinated. Altogether, out of the 94 dried plants, 18 floated for above 28 days; and some of the 18 floated for a very much longer period. So that as 64/87 kinds of seeds germinated after an immersion of 28 days; and as 18/94 distinct species with ripe fruit (but not all the same species as in the foregoing experiment) floated, after being dried, for above 28 days, we may conclude, as far as anything can be inferred from these scanty facts, that the seeds of 14/100 kinds of plants of any country might be floated by sea-currents during 28 days, and would retain their power of germination. … The average rate of the several Atlantic currents is 33 miles per diem (some currents running at the rate of 60 miles per diem); on this average, the seeds of 14/100 plants belonging to one country might be floated across 924 miles of sea to some other country, and when stranded, if blown by an inland gale to a favorable spot, would germinate.
Subsequently to my experiments, M. Martens tried similar ones, but in a much better manner, for he placed the seeds in a box in the actual sea, so that they were alternately wet and exposed to the air like really floating plants. He tried 98 seeds, mostly different from mine; but he chose many large fruits and likewise seeds form plants which live near the sea; and this would have favoured both the average length of their flotation and their resistance to the injurious action of the salt-water. On the other hand, he did not previously dry the plants or branches with the fruit; and this, as we have seen, would have caused some of them to have floated much longer. The result was that 18/98 of his seeds of different kinds floated for 42 days, and were then capable of germination. But I do not doubt that plants exposed to the waves would float for a less time than those protected from violent movement as in our experiments. Therefore it would perhaps be safer to assume that the seeds of about 10/100 plants of a flora, after having been dried, could be floated across a space of sea 900 miles in width, and would then germinate. The fact of the larger fruits often floating longer than the small, is interesting; as plants with large seeds or fruit which as Alph. de Candolle has shown, generally have restricted ranges, could hardly be transported by any other means."
Darwin also performed germination tests on seeds found in soil caught in the roots of drift timber thrown up on beaches of islands. He tested seeds from the crops of bird carcasses.
"…peas and vetches, for instance, are killed by a few
days’ immersion in sea-water; but some taken out of the crop of a pigeon,
which had floated on artificial seawater for 30 days, to my surprise nearly
all germinated." He studied seeds from live birds. " I have never seen
an instance of nutritious seeds passing through the intestines of a bird;
but hard seeds of fruit pass uninjured through even the digestive organs
of a turkey. In the course of two months, I picked up in my garden 12 kinds
of seeds, out of the excrement of small birds, and these seemed perfect,
and some of them, which were tried, germinated. But the following fact
is more important: the crops of birds do not secrete gastric juice, and
do not, as I know by trial, injure in the least the germination of seeds;
now after a bird has found and devoured a large supply of food, it is positively
asserted that all the grains do not pass into the gizzard for twelve or
even eighteen hours. A bird in that interval might easily be blown to the
distance of 500 miles, and hawks are known to look out for tired birds,
and the contents of their torn crops might thus readily get scattered….
Seeds of the oat, wheat, millet, canary, hemp, clover, and beet germinated
after having been in the stomachs of different birds of prey; and two seeds
of beet grew after having been thus retained for two days and fourteen
hours.
…
I forced many kinds of seeds into the stomachs of dead
fish, and then gave their bodies to fishing eagles, storks, and pelicans;
these birds, after an interval of many hours, either rejected the seeds
in pellets or passed them in their excrement; and several of these seeds
retained the power of germination. Certain seeds, however, were always
killed by this process."
Darwin went on to discuss seeds he found in soil stuck to the feet of birds:
"Prof. Newton sent me the leg of a red-legged partridge (Caccabis rufa) which had been wounded and could not fly, with a ball of hard earth adhering to it, and weighing six ounces. The earth had been kept for three years, but when broken, watered and placed under a bell glass, no less than 82 plants sprung from it: these consisted of 12 monocotyledons, including the common oat, and at least one kind of grass, and of 70 dicotyledons, which consisted, judging from the young leaves, of at least three distinct species."
Excerpts from Charles Darwin’s The Origin of Species, 1859.