Annals of the New York Academy of Sciences
Volume 57, Parental Age and Characteristics of Offspring pages 484–487, January 1954
Erwin Bünning

Many species of plants show no signs of aging in their growing points, while other species show distinct processes of aging. These processes may be very slow as, for example, in many species of Bambus and Agave, or in several types of palm trees, where it takes some years before the growing points show manifestations of aging. This aging becomes apparent by the diminishing size of the leaves and, very often, by the fact that only flowers appear. The formation of flowers is suppressed by the leaves as long as new leaves are formed; that is, as long as the plant is comparatively young.

There exist, also, species of plants, the aging of which is not continuous but rhythmical. In these cases the individual plant shows inactivations and depressions of life activity which are, in all respects, similar to the beginning of the type of aging mentioned above. In the case of periodic aging, however, these depressions are only temporary. They are followed by a rejuvenation. We need only mention, as an example, the perennial plants of temperate regions with their annual period of inactivation during the winter. There may be some doubt as to whether these periodic inactivations are comparable to the inactivations which actually lead to death. But these doubts are removed, not only by investigations on the physiological similarity between the depression of life activity during the fall, and preparation for death, but also by the fact that, in the case of reversible inactivation, many parts of the plant; leaves, stems, etc., indeed often all parts, except rhizomes or bulbs, actually do die. Thus the annual period of inactivation or rest is a phase of aging which leads in some parts to death, in others only to inactivation followed by rejuvenation.

In this type of plant, the surviving parts show a gradual decrease of life activity in the fall, and a gradual reactivation during the ensuing months. We know, definitely, that this periodic aging and rejuvenation is not merely induced by the fluctuations in the external factors, but is distinctly an autonomous process, which also goes on under constantly controlled, or laboratory conditions.

It is a surprising fact that the seeds ripening on these plants may continue to show, during their time of connection with the mother plant and during the following months (that is, during their rest period), the same inactivation and reactivation as the mother plant. This is clear, at any rate, with the seeds of several species. The consequence of this dependency is that a seed from an early flower (that is, a seed ripened during the spring or early summer) has quite different qualities compared with a seed from a later flower. These differences may be found, especially, when testing the germinative qualities. It is a well-known fact that the seeds of many plants show a period of dormancy during which no germination or only a very delayed germination, is possible.