EXPERIMENTAL ECOLOGICAL GENETICS IN PLANTAGO. V. COMPONENTS OF SEED YIELD IN THE RIBWORT PLANTAIN PLANTAGO LANCEOLATA L.

The study of the manner in which plants vary in their seed yield has usually been the province of agronomists and plant breeders interested in crop production. Such studies have used the approach of partitioning yield into a number of components, and then examining causes of variation in the individual components as well as the interrelationships among them (for discussion see Adams, 1967; Grafius and Thomas, 1971). These yield components may be morphological or physiological attributes. Frequently, emphasis is placed on the "major" yield components, namely weight per seed, number of seeds per fruit, number of fruits per inflorescence, and number of inflorescences per plant. Together these major yield components multiplicatively determine total weight of seed per plant, a commonly used measure of yield. The methods and concepts employed in the analysis of yield components can be applied to analysis of components of fitness in natural populations. Thus the amount of resources allocated by the plant to seed production (seed yield) is directly related to its reproductive output (number and size of seeds), and, in that these resources are no longer available for growth and survival, the amount devoted to seed may be inversely related to longevity (Gadgil and Bossert, 1970; Primack, 1979). With regard to components of seed yield it is surprising that the study of yield components and their interrelationships have been largely confined to an agronomic context. The few studies that have been done on natural popula-