Ontogenetic and Anatomical Studies of the Flower and Fruit of the Fagaceae and Juglandaceae

Abstract

1. In both the Fagaceae and the Juglandaceae the ovary develops as a fleshy, urn-shaped tube (the product of conjoint growth of stem and carpels), bearing on its rim perianth and stylar components. A cauline placental axis growing conjointly with the inturned carpel margins produces the septa of an ovary, which is incompletely triloculate in the Fagaceae and biloculate in the Juglandaceae. 2. The involucre is cupular and consists largely of fleshy axis. In the Fagaceae the involucre incompletely incloses the ovary as a ringlike swelling beneath the flower, bearing numerous acropetally developed scales; in the Juglandaceae it completely incloses the ovary and is united with it, forming the fibrous-fleshy indehiscent husk of the walnut and the 4-valved dehiscent husk of the hickory nut. 3. The persistence in the Fagaceae-Juglandaceae series of inner and outer fleshy regions alternating with a stony layer in the seed-incasing body suggests a pattern well defined in the gymnosperms, even to the cupule-inclosed seeds of the pteridosperms, except that both protective and nutritive functions have been to a large extent transferred from a highly differentiated seed coat to the ovary wall and involucral structures. The outer fleshy layer (in the Fagaceae and Juglandaceae, involucral axis) may or may not be united with the stony section of the ovary, while the inner fleshy region (endocarp) eventually becomes dry and chaffy, and in the walnuts almost indistinguishable. 4. A marked reduction in the number of foliar appendages borne by the stem axis beneath or immediately adjacent to the flower as well as a closer association of such as do appear, in combination with other specialized characters (for example, reduced number of carpels and ovules), point to a more advanced position for the Juglandaceae than for the Fagaceae. 5. On the other hand, fundamental resemblances in the floral structure of these families, including the catkin arrangement of unisexual flowers; the axial character of ovary wall and placentation; and the major role played by the involucral encasement of the flowers and fruits, argue in favor of their somewhat close alignment in any phylogenetic arrangement of the flowering plants.