Frontiers of Science: Plant Prospecting


Plant Prospecting

Extinction sounds like a very final word. The dictionary defines it as a state of annihilation, of having died without leaving any descendants to carry on the species. But for some plants now considered extinct, this condition may be only temporary.

A case in point is the tree Sophora toromiro that once flourished on Easter Island, where it provided the natives with wood for their houses and canoes. With the introduction of sheep to the island in the eighteenth century, the number of trees declined because the sheep gnawed at the bark of the trees and ate its seedlings. The tree population diminished to the point that by 1962 not a single specimen could be found. The S. toromiro was listed as being extinct.

Several years before that time, however, the famous explorer Thor Heyerdahl had visited Easter Island and had collected some S. toromiro seeds that he deposited at the Göteborg Botanic Garden in Sweden. Just this past year three of the seeds sprouted and began to develop into normal plants, and scientists are now looking into the possibility of reintroducing the tree to its previous natural habitat on Easter Island.

This is just one example of the amazing ability of seeds to germinate after long periods of dormancy. There are others, of course. Perhaps one of the most remarkable examples was the study conducted by a Danish botanist, Soren Odum, who took soil samples out of the remains of an archeological site in northwestern Jutland dating from at least 1,700 years ago. With careful procedures he was able to germinate four seeds that produced weeds common to that period of time. He also grew plants from many 600-year-old seeds obtained from other archeological excavations.

The ways in which seeds buried in the ground are able to survive for such long periods of time are not completely understood. It is believed, however, that the presence of moisture in the soil allows the seeds to maintain a low level of activity just sufficient to make minor repairs to their cells. Why they do not germinate and die underground is also not completely understood, but it appears to be a lack of light that inhibits their sprouting at depths too deep to allow their penetration to the surface. Scientists are keenly interested in unraveling the mysteries associated with the potentiality of seeds. They may hold the key to developing better storage procedures for seed stocks required for plant breeding programs.

Perhaps the most interesting aspect of the longevity of seeds, however, is the very real possibility that many plant species long believed to be extinct may be brought to life again by what we may call “plant prospecting.” Although the term is new, the concept has a long history, reaching back at least to 1859. In that year, an old house constructed well before 1700 on land owned by the governor of Massachusetts had been torn down. The famed naturalist Henry David Thoreau carefully searched through the exposed cellar for plants that may have sprouted from seeds long hidden from the light of day. Indeed, his stated goal was “to reproduce long extinct plants.” His results—“a species of nettle which I had not found before; dill, which I had not seen growing spontaneously; the Jerusalem oak, which I had seen wild in but one place; black nightshade, which is quite rare hereabouts; and common tobacco, which, though it was often cultivated here in the last century, has for fifty years been an unknown plant in this town.”

Here, then, is a real opportunity for anyone who wants to embark on a true adventure. Try your hand at plant prospecting. Seeds are literally everywhere. Indeed, it has been estimated that common ground may contain as many as 100,000 dormant seeds per square meter. With a little thought for searching out unique places, you might unearth and nurture back to life a plant that is now thought to be extinct. So organize a safari, even if its destination is only somewhere right in your own hometown, and “bring ’em back alive!”

[illustration] Illustrated by Dick Brown