The Number of Seeds Produced by Certain Plants

Abstract

Although there have been several studies of the number of spores, seeds, or fruits produced by various plants, for the great majority of our common wild plants little or nothing is actually known about this subject. The following notes may therefore be of interest. In May, 1956, I transplanted from woods in Robert Allerton Park, near Monticello, Piatt Co., Illinois, one plant of giant hyssop, Agastache nepetoides (L.) Kuntze (Labiatae) to my garden in Urbana. This plant soon grew about six feet tall and developed twenty or more lateral branches. It produced flowers continuously for about four months, from July until the end of October and the beginning of November. Toward the end of the flowering period I counted 48 inflorescences on the plant. The average number of whorls of flowers in each inflorescence was 32, with an average number of 42 flowers in each whorl. It is well known to botanists that the pistil of flowers of the mint family is bicarpellate. Early in its development a constriction appears in the ovary dividing each carpel into two locules. Each locule has one basal erect anatropous ovule, and the fruit is a group of four achenes or nutlets each containing one seed, if all mature. Hence it will be seen that if the plant under observation produced an estimated number of 64,512 flowers, the possible total number of seeds would be approximately 258,048 or something over a quarter of a million. It should be noted, however, that the number of seeds produced under cultivation is probably higher than that produced by most wild plants, as cultivated plants may attain a larger size, and their flowering season may be longer. Calculations made from herbarium specimens are likely to indicate a somewhat smaller number of seeds, as such specimens are usually taken from smaller plants in prime flowering condition, with shorter and less mature inflorescences. In any case, only a small part of the full grown plant can be made into a standard herbarium specimen. By way of comparison, the average number of corn plants (Zea mays) per acre in Illinois is said to be about 12,000. If all the seeds from one giant hyssop germinated and were planted in rows like those of maize, the number of plants would be sufficient to fill a 21-acre field.